Authors Prof. Dr. Kęstutis Zaleckis, Assoc. prof. Indrė Gražulevičiūtė-Vileniškė, Jurga Vitkuvienė
The Technical University of Kaunas*
Looking at architecture or urban structures and exploring them in different contexts, the focus is on volume and form, and the space between architectural volumes and boundaries is most often seen as emptiness. Bill Hillier, who, in the eighth decade of the last century, built the foundations of the space syntax model, relied on the statement, that there are spaces of various cultural, social and economic processes from the point of view of architecture and urbanism. This postulate can be logically expanded or extended by stating that each culture, period, or social group is characterized by both, individual scenarios or by common life scenarios. These scenarios transferred to space by formatting it with architectural tools and connecting with other spaces. On the other hand, based on the science of semiotics (asserting that a person perceives and uses his entire activity on the basis of his objects as a text) and Michael Cole’s Theory of Cultural-Historical Psychology (developing the general statement of semiotics on the concept of cultural-historical artifacts and the collective theory of external consciousness), it can be said that architectural space with its own configurations and connections with other spaces itself forms or at least promotes certain practices of its use. Some historical examples:
- The Islam city of the middle ages as a labyrinth of narrow transitions, reflecting the cultural aspiration to maximally separate the private space from the public, to promote social contacts with westerners in spaces of almost intimate scale. This feature, by spreading of Islam, is treated as a model for introducing a new way of life in conquered countries..
- The medieval city in Western Europe of the Gothic Plan with the narrow streets, that emphasize verticality, in whose space network obviously does not distinguish any street. Its center is a medieval enclosed square, and the city (according to Jaques Le Goffo), which by the wall of many meanings stands out from the medieval culture, physically and spiritually unsafe in the seen countryside environment. According to Lewis Mumford, it is a city of religious processions, in which the street space makes its spectators even observers; where the network of equivalent streets creates the conditions for a relationship between private and public space, which is important for an individual economic initiative inherent to Western culture and, according to Max Weber, the culture that opens and encourages it. In common, the three equally dominant (cathedral, town hall, castle) and the corresponding spaces adjacent to them reflect the balance between the three powers, and so on.
- The classicist cities of Western European reflect completely different scenarios and values for space usage. A good example is Versailles, created in a “flat spot” and perfectly reflects the culture of that time. According to Mumford, during this period the palace was an example for everything and as the center of the city and the world. Accordingly, the city streets begin to spread, allowing carriages and horsemen to move without hindering the pedestrians. The most important spaces lead to the palace, the representative squares that have emerged in Renaissance are being developed, whose primary function is not trade or another gathering of people, but creating the right background for the palaces and emphasizing of their importance. The most important streets are planted by trees, in order to reflect the lifestyle of the palace next to the park. Trading is concentrated in the market squares created for that purpose. Similarly, the economic and servants’ parts are separated as in the palaces or in the copied residences from the representative space and so on.
In the history of urbanism, there are many similar examples that make it possible to talk about a peculiar reading of the urban landscape as a cultural artifact based on its spatial characteristics. This reading is important for both, the representative of a particular culture using spaces and for the guest who wants to know them better. It is logical to state that the properties that determine the readability of the urban landscape as a cultural and social scenario are essential (or at least very important) in terms of its cultural identity. The concept of urban landscape spatial “legibility” and “readability” can be formulated hypothetically at this place. The first, by analogy with the written text, would only show the perception of the spatial structure, and the second would include the recognition of potential usage scenarios, thus ensuring the “text” attractiveness or interest to the reader. An example showing the difference: basically, probably each space created by architectural measures is more or less “legible”, and “reading” is also based on associations, that are emerging in our minds with possible common space usage scenarios.
Is it possible to investigate urban landscape readability, can it be done based on quantitative models? What models, even if the term “readability” is not used, do it?
The review is worth starting with the fundamental concept of the topic in question, talking about the essence of the relationship between the observer and the urban space network – is Benjamin Walter’s idea of secular pilgrimage. According to it, the city, because of its specific spatial structure and its people and their activities, becomes the object of pilgrimage – a pilgrimage whose purpose is to discover and perceive itself because of unexpected associations, connotations, memories, experiences, and so on. Although Walter’s concept does not talk about urban landscape readability, but the spatial urban environment is seen as very important, seen as the text which is worth the pilgrimage trip, in which both space and its fill are important.
Environmental psychology talks about a psychologically acceptable environment – an environment in which a human chooses to live and be, if he has a freedom of choice. It is important that, according to the authors of the theory, long-term presence in an environment that is not acceptable can cause a variety of psychological ailments. Four characteristics of the psychologically acceptable environment:
- Coherence – all the details of the environment form a perceived integrated whole.
- Complexity – emphasizes the need for typological diversity of the elements that form the environment.
- Mysteriousness – the environmental feature that allows it to look slightly different each time without losing the other two properties. It is interesting mysteriousness can be achieved by various means: by creating urban areas which gathering mostly people and allowing them to observe new faces and their activities every time when they visit; by creating a “labyrinth” in the city, where you can easily “get lost” and discover something new; by integrating the natural environment into the city, etc.
- Legibility – a property directly related to the subject of this text, which means that the spatial environmental configuration is easily perceived. Although it is identified as the last, it can be seen as the basis for the expression of the other three attributes.
This model can be applied to both natural and urbanized environments (and most importantly, it is essentially linked to quantitative landscape characteristics). For example, the qualitative characteristics of the natural landscape are associated with quantitative indicators such as the number of different elements in the field of view, the size ratios, density, etc.
Probably, the mental view of the city of Kevin Lynch’s is known to all architects. This is one more model that is closely related to urban landscape readability. It identifies elements of a conceptually perceived city’s physical body (roads, nodes, landmarks, borders, and areas), that can, in principle, be interpreted as archetypal elements of the city’s “text” perception. The successful use of the elements of this model for creating a more psychologically acceptable environment in Kaunas (contributing to the greenfield of the urban structures by assuring all four characteristics of the psychologically acceptable environment) confirms a certain connection with its readability.
Gordon Cullen according to the concept of perception or vision of a series of spaces (serial vision) examines how the human consciousness structures the city landscape from the “inside”, i.e. by moving in it. Based on this theory, the relationship between the “here” and “there” is the essential link that describes the urban landscape structure. “Here” is an area in which an observer is at a certain time, “there” – an area in which he can move. “Here” – always known and visible, “there” – can be both visible and invisible. Many architectural features of space are associated with how “there” space is created, visible or invisible, how the “here” limits are defined, how the attention of the observer is diverted from “here” to “there,” and so on. It can be argued that the connection between “here” and “there” leads to a greater or lesser degree of legibility or even readability of the environment. The most important perceived spaces form the “lifeline”- functionally and compositionally distinguish the backbone of the city or its part in the environment, which can be named as the most legible part of the city and is associated with the Lynch city mental image roads, landmarks and nodes.
The intelligibility of the spatial structure of the city, as a specific and important feature of the spatial structure of the city, Bill Hillier, describes it as a correlation between important locals, the best places which can be reached on foot and the largest streams of people attracting places and common city centers. Correlation, in this case, means that urban spaces that are important in terms of local, spatial configurations and functional potentials coincide with important common urban spaces, and the majority of pedestrians perceive the most important part of the city. The orientation towards the most important and most influential spaces of people flows is related to the more intensive street culture as the main manifestation of the city and, according to Mumford, can be developed by linking it to both the ideas of secular pilgrimage and the psychologically acceptable environment already mentioned in this text.
Even closer to the quantitative model of reading, Nikos A. Salingaros approaches, formulating three optimal integrity and, at the same time, from the point of view of the perception of the law of architectural composition:
- The first law states that the integrity of an architectural composition on the smallest scale is provided by contradictory tensions, for example, white-black, open-enclosed, high-low, etc. In this place, you can also have an interface on here-there model, discussed earlier.
- The second law states that, on a larger scale, the integrity of a composition and its, as a whole, readability are ensured by similarity: shapes, colors, volumes. However, some degree of irregularity or slight destruction of similarity, according to Salingaros, increases the interest of the composition – this is related to the concepts of mystery and diversity in environmental psychology.
- According to the third law, the ratio of adjacent sizes of different scales must be equal to or close to the Euler’s number (Napier’s constant) e – 2.7.
These three laws are supplemented by the statement that the compositional and functionally important parts of the architectural object must coincide in order to make the structure more perceived or readable. This, in relation to building facades, broadly corresponds to the concept of “lifeline” already mentioned in urban planning. Based on three laws, the index of perceived optimality of the architectural composition is also proposed, which shows the balance between the symmetry and the asymmetry of the building’s facade.
The last concepts discussed — the model of cognitive frame building created by John Peponis – is most appropriate for the problem under discussion: it is oriented to the analysis of space in terms of its perception. This model is complex because it takes into account two types of perceived urban environment – moving and static observers. It is accurate, based on quantitative indicators, also is largely adapted to the urban environment, and at least partially combines some of the ideas already discussed. The model is based on the basic statements of the visual graph analysis – of the space syntax and on its particular part. According to them, both the building and the city’s space must be seen as tanks of social and cultural processes that form a unified network. The functional spatial potential is largely determined by its local network – it is by how many spaces it is directly connected to, how well it is accessible, how often it is chosen as a transit space, and so on. The mathematical network representation is a graph, and the quantitative indicators support the calculation of the significance or centrality of the vertices of the graph, for example, the centrality of remoteness is equal to the sum of vertex distance to all the remaining vertices. The lower this number is, the vertex is better in reaching it in the entire network. If the street segments (segmental angular analysis of space syntax) are modeled as the vertex of the graph, then the spaces with the said minimum numerical value usually represent the center of the city. The vertices become the “cells” of the research area in the visual graph, which are defined by dividing the plan of the research territory into an equal step grid by equal parts. If from one such cell is visible another cell and can be moved to it directly without changing the direction of movement, they are considered to have a direct network connection.
According to Peponis, the four models of the cognitive frame model are:
- Direct purview. It is written in the formula: DP(x) = (Σn + 1) m2, where Σn is the sum of all nodes visible from the node x, to which you can move in a straight way. The indicator basically shows the visible and directly accessible area.
- Path elongation. It is written in the formula PE(x) = Σ (l – l0)/l0, where l is the real the shortest path in several meters between x and y, and l0 is the straight path between x and y, if space is not obstructed. The indicator tells how much of a particular investigated structure departs from the road archetype and approaches to the labyrinth.
- The average number of turns is calculated according to the formula MT (x) = Σt / (n – 1), where Σt is the sum of the turns moving from x to all remaining vertices, n is the number of vertices. The indicator is somewhat similar to the path elongation, but complements it and helps to understand more precisely person’s perception of distance. The point is that, according to spatial syntax, a person can feel the distance both in length units and turns. Which of the distances becomes more relevant in a given situation is determined by many factors, but the ability to consider both of them in one model is an undoubted advantage.
- The length of the path between the turns is calculated by the formula PLT (x) = Σl / MT, where Σl – the average length of straight sections passing through x, MT is the average number of turns. In essence, the indicator tells which mid-length axes crosses the network points. For example, the indicator will be substantially lower in Fez’s Old Town, which reminds the labyrinth, larger in the city of the Gothic plan and even more larger in the city of the classicist plan.
It is worth mentioning that the discussed cognitive frame model has been successfully tested by predicting and evaluating acceptable, one of the valuable qualities of the urban real estate cultural heritage objects – spatial structures – changes in the territory of the former artillery town of Kaunas fortress. More features can be found on the interfaces of the spatial syntax visual graph with urban landscape readability testing without using the John Peponis model.
Urban spatial structure readability
With the introduction of this model in territories with several different both in size and in spatial characteristics, two problems were encountered: it is not possible directly to compare numerical values of the same indicators between territories of different sizes, while the four indicators are hardly perceived and requires a more generalization without losing the produced complexity of the indicators. In solving the second problem and in accordance with spatial semiotics statement that the essence of architecture as space structuring art is part of space demonstrations, while part of the spaces is a hiding action, two new indicators were proposed according to two types of space users: Dynamic Demonstration (DD) and Static Demonstration (DS). In general, these indicators are called readability, bearing in mind that they must show not only the intelligibility of spatial structure configurations but also their perception of the social content container, for example, according to Hillier, three turns indicate the location of a local center. New indicators are written using the appropriate formulas:
DD = MT × PE,
DS = DP × PLT.
Thus, the smallest numerical meanings of dynamic demonstrations show that public spaces of the city, which are accessible from all remaining areas of the investigated territory by changing the direction of movement in minimum times and by minimum derogation from the straight lines connecting the start and end points of the movement.
The maximum numerical values of the static demonstrations show those spaces in the urban structure, which are of the largest area and have the longest axes through them.
In solving the problem, related to the size of different territories, a way to normalize DD and DS values was sought. Several ideas have been developed and tested. The first concept is as follows: the normalization process should be based on a comparison of the current numerical demonstration or its four normal component values with possible maximum, e.g. the maximum possible number of turns in the labyrinth can be by the longest axis in the area under investigation, and so on. In order to verify the normalization model, calculations were carried out with more than twenty historical cities or parts of them expressing essentially different genotypes of the urban space in their most purest form: Tunisia, Damascus, Fes and Sfax as examples of medieval Islamic cities that demonstrate cramped socially integrated spaces and at least at first glance confusing structure of labyrinth type; Vilnius, Krakow, Berlin and Kaunas old cities as examples of European medieval cities; Zamosc, Palmanova, Nove Zamky, Sabbioneta as Renaissance cities; Versailles, Edinburgh New Town, Kaunas New Town and Christopher Wren’s prepared London Plan as Classical Planning Cases; Le Corbusier prepared “Plan Voisin”, Brazil, Kalniečiai and Silainiai in Kaunas, Elektrėnai and Visaginas as examples of modernist urbanism. After many normalization tests, it turned out that the proposed idea does not produce the desired result: it does not appreciate the fact that, although visible, but a large space is only legibility as a configuration, but not readable as a potential social content carrier, and differences between urban genotypes are reflected not sensitive enough, the numerical value scale itself is “squeezed”, close to zero and hardly perceptible. In addition, the configuration of the boundaries of the investigated territory affects maxima of some indicators, e.g. such as the longest possible length of the section or the number of turns. The second idea of normalization was based on a comparison of the readability of the city with the benchmarks. We were trying to select both specific cities (Brazil and Fes) and hypothetical (“Plan Voisin”). At the same time, it was attempted to “fit” the reference structure on specific boundaries of the investigated territory. Unfortunately, and in this case, it turned out that the size of the investigated territory continues to affect the normalized numerical values of the indicators. By choosing one or another benchmark, there is always the likelihood that a more appropriate example will be found, and the result is too sensitive to the fact as the benchmark is “put” on the investigated territory. Equally important is the fact that the two mentioned tests of normalization in principle, did not focus on the measurement of social space, so, perhaps speaking more about legibility than readability.
In the third test, selecting the human as the basis of the view, it was taken into account that the four readability components need to be normalized individually, and the readability / non-readability of the space depends not only on the configurations of the space but also on its social dimensions. In this way, the largest radius of the socially readable territory was chosen at 137 meters.This distance is also used for readability of urban axes, only by increasing it accordingly – it was based on Cullen’s “here and there” as a model of a legible city street spaces, i.e. if there are no other boundaries, the radius of 137 meters defines the readable “here”, and an additional 137 meters – readable “there”. The normalization of the path elongation was based on an empirical test, which found that 20% elongation of the path, comparing it with straight, human does not still perceive as an elongation. According to Hillier’s study (that three turns are often perceived as an optimal distance to a local urban center), the three turns were selected as socially-readable maximum turning number. The normalized scale for each indicator in the analyzed cases varies from 0 to 30. The most important part of the scale from 0 to 1 shows readable spaces, where 0 approaches to personal space sizes (for example, the short section of the narrow streets of the medieval Islamic city between the turns), while 1 – near the maximum space is still perceived as a possible social content container (for example, the medieval market square). The upper limit of the scale, far exceeding the unit, can, in principle, be limited in the future in terms of visual perceptions, for example, such as the distance from which a human figure is recognized.
Figure 1 The Schemes of the Normalization Idea
Particularly normalized values are calculated as follows:
- The DPnorm of a specific graph vertex is equal to the directly connected, or otherwise visible and accessible, moving in a non-changeable direction, the number of vertices plus one and vertices, reached in the radius of 137 meters from the calculated node, to the ratio of the number. Without using the terms of the graph model, this is the ratio of the visible area of the space point and the area reachable at a radius of 137 meters.
- PLTnorm the unregulated PLT calculated using the formula above is calculated by dividing it from 548 meters, i.e. 137 meters distance, multiplied by four. This corresponds to the spatial schema “here and there” seen to both sides from the point.
- PEnorm for each specific pair of points in the space by dividing the path elongation (PE) among them from the straight distance between the same points, multiplied by 1,2. Final mean normalized elongation, moving from a specific point to all remaining points in the network, is obtained by summing trips from it to all remaining points elongation in the network and by dividing them from the total number of points.
- MTnorm is obtained by dividing the value of MT from three.
Graphically, the idea of normalization is shown in Figure 1.
It is worth paying attention to the description here, that the architecture described in space semiotic research as an art “demonstrate” or “kill a chaos monster”, separating one space from the other, one of them exhibiting, while the other hiding. The demonstration is achieved through an essential pairs of contradictions, helping for the consciousness to structure the environment:
- “Open-enclosed”. Based on a pair of perceived contradictions in this environment, the visual graph is formed and the DP index is calculated. It is important that the proposed normalization introduces the social dimension of the area readability which is not typical for the original model.
- The already mentioned “here and there” as a representation of possible serial perception lines, which in the proposed model normalizes the PLT indicator, taking into account social distances.
- “Static-dynamic”. This pair reflects two ways of interacting with the environment. The sizes of the perceived space from the static position are normalized as the DP and PLT indicators mentioned above; the dynamic perception is represented by the normalization of PE and MT indicators, reflecting two basic distance measurement methods peculiar to human. The proposed calculation of a dynamic and static demonstration combines these four indicators in a complex manner, making them more easily perceived and allowing one of the readability ensuring features of the space to be compensated by others.
- “Demonstration-Hidden” or “Readable- Non-Readable” in essence, are defined by both the four normalized and the two new indicators.
Thus, the improved cognitive frame model describes the complexity of the readability of the urban space.
The final formulas for normalized demonstrations are written as follows:
DDnorm = MTnorm * PEnorm,
DSnorm = DPnorm * PLTnorm.
The above-disclosed definition is revised: the normalized smallest numeric values of the dynamic demonstrations from 0 to 1 represent the public spaces in the city, which are accessible from all remaining spaces of the territory under investigation by changing the direction of movement not more than three times and not exceeding the deviation from the straight line between the beginning and the end of the trip by more than 20%.
The numerical values of the normalized static demonstration between 0 and 1 represent those spaces in the urban structure, the radius of which does not exceed 137 meters and which are crossed by axes not longer than 548 meters, i.e. from each point on both sides is visible one “here” and one “there” a social-sized space.
Exceeding the unit, the part of the scale in both cases indicates, how much public spaces are not perceived as social spaces.
According to it, that the relative part of the public space area in the city is related to the intensity of its use, the third was proposed – the intensity indicator, which is calculated by dividing the graph area of the public spaces from the total investigated area of the territory. It is logical to expect the highest intensity to be found in medieval structures, where the streets have performed many functions: communication, leisure, shopping, and so on. The smallest – in modernist regions, where the space is much more specialized, for example, for children’s playgrounds, for peaceful rest, for cars to park, for moving, etc. Intensity is also linked to the aforementioned one of the essential features of the city, according to Mumford – the street culture and, probably, indicates its potential diversity and activity.
The proposed normalized model tested in two stages. In the first stage, based on two fundamentally different or even opposing examples of the influence of their spatial structures on street cultures, it was sought to see if the model responds to such differences. The first example chosen for the investigation is the Medieval Gothic city structure, represented in the 13th century Berlin Plan. Urban historians consider such a structure to be considered as enclosed or social interaction and relation with the environment – introverted, with low differentiated public spaces and the entire structure- the all streets of the city and the filler of volume is equivalent in functional and logistical terms in all city territory; such street of the city is an intensely used public space that brings together all possible activities. The second example is “Plan Voisin”, which was ready for the reconstruction of the Paris Center in 1925. as a benchmark with encoded features of modernist urbanism: specialized spaces, an open structure, dividing people and activities, and free layout of buildings in the space.
What do readability calculations mean? Would it be only looking at them and without seeing the city plan, or would it be possible to understand the aforementioned peculiarities without knowing its scale? Looking at the Berlin indicators, we see that there is an essentially very socially spatial structure: DP (here is what goes on in the text, the normalized values of the calculated indicators) the mean value reaches 0.3 and only individual maxima reflecting the straight track of the streets typical to the Gothic plan reaches 1.2. If the so-called spontaneous or organic plan of a medieval city would be investigated, the maximum of this indicator would be significantly lower. Here should be remembered that according to the normalized scale, the unit represents the maximum socially readable intermediate between the introverted (i.e., socially recognizable and inclusive) and extroverted (are generally perceived as a transit space or field, but not a place where people are concentrated in joint activities) configuration. Correspondingly, the approach to zero corresponds to the increasing degree of intimacy of the space. It, if compared with medieval Berlin, should be much smaller in the already mentioned medieval Islamic cities, where, perhaps, and the claustrophobic space has performed many functions for the medieval Western European occupant, starting with the promotion of social contact, ending with the separation of residential quarters from the commercial part of the city. The straight path elongation (PE) does not exceed a unit, and that essentially perfectly reflects the democratic structure typical to the Gothic plan, which provides many equivalent alternatives, based on a regular rectangular street network. Again, by forestalling, we will compare the situation with the Islamic cities, we will see that the indicator is higher and exceeds the unit, thus reflecting the network of “tree-crown” streets, in which you may need to go to the “trunk of the crown”, even if you want to enter the street on the other side of the block. Functional and composite urban axes (PLT) range from 0.12 to 0.38, not only by showing the well-perceived spaces “here and there” but also two more likely things:
- The relatively small size of the city: it has already been mentioned that the upper limit of the normalized scale can be largely determined by the size if we talk about the case of a permanent structure, i.e. the city of straight streets, which in essence should be the ideal city of the Gothic plan. This addiction can be eliminated by introducing a maximum distance limit in terms of visual perception, but in this case, the possibility of deducting information in a model about the size of a city or part of it is quite valuable.
- The second characteristic of the city is likely to be shown -this is a certain deregulation or distortion of the straight street network, which may be due to adaptation to local conditions or transformations over time.
Interestingly, In the case of Berlin, both statements are correct. The average number of turns is 0.9 and the maximum is 1.9. On the one hand, this confirms the proximity of urban spaces to each other, which is perfectly felt when moving around in a such plan type old towns – many of the desired streets can be reached by reversing the direction of the movement three times, which, according to Hillier’s study, is understood as a local distance or a part of the urban structure “here.” What does mean a slight increase in the indicator’s maximum? This shows that in the urban structure we will probably find the roots of the “tree crown” plan or rudimentary. In Berlin, they are represented by blind alleys, which have access to the river.
Let’s look at “Plan Voisin”. DP average values reach 7.3, this allows us to say, that the structure is essentially similar to the field or at least will be perceived as such one. The PLT indicator is well above Berlin: the average values increase from 0.234 to 1.518 and the maximum is from 0.376 to 2.086. In both cases, we have a fundamental contrast – a social, introverted structure against antisocial and extroverted. In both PE and MT, we see significantly lower indicators in Paris, very close to zero. This indicates that in the area under investigation it’s possible to move almost like in the “open field”. If we compare the intensity, then it is equal to 0.25 in the medieval city and 0.9 in the modernist structure. Numbers speak for themselves: in the first case, we can expect a catalyst effect on the street culture of an available limited public space, in the second case, we have a space that offers many alternatives and is probably to be highly specialized.
At first glance, the model has been revised and normalized with a cognitive framework that is quite rightly, so in the second stage it was tested with a much larger number of historic cities in order to find out whether differences between types of urban structures are recognized and whether generalities and different nuances in cities of the same type are seen. Table 1 shows all the indicators obtained
The first group is the Middle Ages of Islam cities, represented by Fez, Damascus, Tunisia and Sfax Old Towns. These are labyrinth-like structures, in which it is difficult to orientate for a stranger, characterized by a cramped space and striving for the best possible separation not only the private space from the public but also residential areas of the city from public and commercial. The research revealed the following main features of the city:
- Average values of DP in European cities ranging from 0.1 to 0.2 (in Europe, respectively 0.3-0.6) are lower than in that time in Europe. Also, the fact that in Damascus and Tunisia the highest values of this indicator are higher, reaching 1.65 (Damascus) and 2.74 (Tunisia), thus moving nearer to the highest values of Kaunas and Krakow’s old towns. In the case of Damascus, this is explained by the elements of the regular network that have formed the remaining and main streets from the Hellenistic period, and Tunisia – a vast not built-up areas close to the defensive city wall.
- The PLT indicator for direct communication arteries is significantly lower than in Europe: the average values ranging from 0.9 to 0.18 (in European cities, respectively, 0.18 in the automatic and 0.33 in the Gothic plan cities). In this case, Damascus stands out for the elements of the regular plan, moving closer to the indicator of the organic plan of the Middle Ages of Vilnius. Tunisia, whose wide open space beside the city wall is of a curved plan and does not differ from the general context.
- All four structures show very close average results by the average turning point (MT) – 2.0, 2.1, 2.4, 2.6, and a socially segregated network of urban spaces.
- The path elongation (PE) indicator is interesting and without giving an unequivocal answer. On the one hand, its mean values are higher than those of European ones – varying from 0.02 to 0.56 (in Europe from 0.17 to 0.26). The difference seems to be lower than expected, however, it seems that the indicator testifies to each urban structure as seeking a certain optimality from the logistic point of view, the inherent order and rationality, despite the seemingly labyrinth-like “chaos”.
- The discussed indicators quite accurately correspond to the numerical values of DD and DS. Cities in both Western Europe and this group the intensity are similar, this apparently shows some optimal minima of this relationship, which is necessary for the city to function. On the other hand, in Islam cities it is possible to talk about differences in intensity, for example, in a market area, it is likely to be much higher, while in residential areas it is smaller. The investigated examples of that European periods are much more coherent. Indirectly, the indicators MT and PE, showing the differences in the segregation of structures, let for us to guess this from the results of the calculations we get. On the other hand, this observation makes it possible to think about the improvement of the intensity indicator or further specification, i.e. its calculation to the investigated part of the city by dividing the territory into a basis of functional or regular step.
It should be noted that the three of the cities discussed (Damascus, Tunisia, and Sfax) are analyzed according to historical maps, in which a certain conditional representation of space widths is possible, and Fez has been explored using modern GIS data. Nevertheless, despite this difference, the indicators are close to each other and at the same time sensitively responsive to individual peculiarities, for example, the already mentioned case of Damascus Old Town. To summarize, it is arguable that DD and DS calculations show statistically well readable small “here” spaces, less readable “there” spaces and a hardly dynamically readable structure.
Figure 2 Indicators of DD in the Middle Ages of Islam cities
The second group is the medieval cities of Europe: already explored in the 13th century Berlin, Kaunas, Vilnius, and Krakow old towns. The results of the calculation are basically close to the Berlin case already discussed:
- DP values are higher than in the first group of cities, but their mean values, ranging from 0.30 to 0.611, indicate a slightly more spacious but socially inclusive and “speaking” spatial city. The great variety of indicator inside the group is associated with somewhat strange but a considerable difference in street widths: In Berlin and in Vilnius they are narrower, and in Kaunas both in 1798. map, and according to today’s GIS data is much wider.
- The average PLT ranges at 0.25, by surpassing the Islamic cities. The exception is the organic plan of Vilnius (0.18).
- PE and MT indicators with averages ranging from 0.17 and 1.0 show closer to each other both the physical distance measured in meters and the sense of distance measured by the number of turns in terms of the spatial network. Here, slightly higher rates are distinguished by Vilnius and Berlin. The first is due to an organic plan, and the second one is due to the split structure of the river, in which the limited number of bridges has to be used to get from one part to another.
- The intensity, as mentioned, is similar to that of the first group of cities. The explanation of that is the necessity for a certain minimum of a public space available for a private area, for the optimal functioning of the city.
- An interesting change in the indicators is seen when comparing Kaunas Old Town in 1798 and 1939: at first glance, the structure is fundamentally unchanged, but there are slightly more open spaces (former Fish Market) and alongside the former Presidency’s stretched and, apparently, extended segments of the streets. In this, though not much, but by increasing, the mean values of DP and PLT are also responding.
Based on the generalized DD and DS indicators, it can be concluded that readability calculations describe the investigated medieval cities as larger groups of people, combining introverted and well-dynamically readable structures, among which there are two distinct types: the structure of a regular and organic plan. The second one is characterized by higher MT, PEL and lower DP and PLT values.
Figure 3 Indicators of DD in the Medieval European cities
The third group – the cities based on classicism or its ideas: Versailles, Edinburgh New Town, Ch. Wren completed London reconstruction project, Kaunas New Town.
What do normalizing indicators say about these structures?
- DP average values range from 1.64 to 2.93, while the maximum value is 11.85. Comparing with the first and second group of cities, we see no longer evolutionary but a revolutionary change – the city transformation of social spaces into an “open fields” In essence, the values of PLT submit the same, ranging from 0.27 average values in the medieval city to 0.78. The highest values of this indicator reach even 1.90. This shows the overall change in the structure of the city not only by expanding, but also by lengthening of the streets, but this elongation, if we compare it with the contemporary modernist urbanism which is reviewed, it is still relatively cohesive. This is explained by the vision of the system of the universality of classicism and Baroque cities as connected axes by visual dominants, which alongside with the size of the city and logistics capabilities, contributes to limiting the length of the axes. On the other hand, the same model determines the hierarchy of streets and the marked differences between long streets leading to chambers or other representative places, as well as shorter, residential or farm entrances to the streets serving the plots, which are well visible in the Edinburgh New Town Plan. Accordingly, the average length of two streets also yields a higher, but more moderate result compared to the Middle Ages. Attention is also drawn to the fact that in this group of urban DP the highest and average values differ considerably more than in the two previous groups – it perfectly reflects the strikingly visible two-layer network structure of the streets in the Versailles plan, consisting of three wide streets leading to the palace and the rest of the narrower residential streets fill which is separated slightly from them.
- PE varies depending on the city and specific street network solutions, for example, designed or not secondary streets near economic entrances, but close to the Gothic plan cities. This is logical given the fact that two types of regular structures are compared. The only exception is London, where the main urban arteries that diagonally cross the rectangular street network, allow this indicator to be further reduced. The same is said and about MT.
Summing up and looking at the meanings of DD and DS, the model shows that the city of classicism is better readable dynamically, but at the same time, at least part of the easily accessible spaces are already non-readable as social spaces. The intensity of the expected usage of public spaces is also decreasing, thus matching or reflecting the proliferation of narrow specialization spaces in the city, for example, representative squares, resident squares, shopping malls for a specific type of goods, roadways separated from the sidewalks, and so on.
Figure 4 Indicators of DD in the cities of classicism
The fourth group is modernist cities: “Plan Voisin”, Brazil (or, more precisely, its central and peripheral parts), Visaginas, Kalniečiai, Šilainiai, and Elektrėnai have already been discussed. Looking at the results, we immediately notice, that these examples are divided into two different subgroups.
The first subgroup consists of “Plan Voisin” and both Brazilian examples. It has “huge” mean values ranging from 4.5 to 12.8, and the corresponding PLT values representing an axis of “anti-social” length from 1.2 to 2.1. Dynamic demonstration components show practically an “empty field”, the mean values of MT vary from 0.26 to 0.49, “bypassing” even the city of the Gothic plan in terms of dynamic readability, while PE averages ranging between 0.02 and 0.05; the intensity reaches 0.90. So, in this case, we are facing with a tendency towards a moderate development that has already begun in the classicism of the cities: the city becomes dynamically readable, but statically it is no longer readable as cohabitation and functional space for people. Perhaps it would be inappropriate to ask if it badly or not in the framework of this text because such a model of the city perfectly corresponds to the idea of a modern city. However, based on the analogy with Nicos A. Salingarso’s suggestion of calculating the visually perceptible architectural optimality of patterns, it can be assumed that, as with optimal visual perception, as well as the perception of the city space by moving around urban spaces, two things are necessary: both the simple perceptibility of the structure and the particular complexity of the structure, increasing its interest. This would be a certain balance between DD and DS in the described readability model. From this point of view, perhaps, the medieval cities are a good example of such a balance, while modernist cities demonstrate imbalance between these two indicators. Of course, this is just a preliminary idea, which needs to be verified through sociological research and investigations done locally.
The second subgroup of the fourth group consists of Šilainiai, Kalniečiai, Visaginas, and Elektrėnai. Their more moderate indicators perfectly reflect the transformations of modernist urbanism, adjusting to a more local scale and creating more social spaces and looking for more interesting and individualized spatial solutions. Interestingly, that the Visaginas planned by a non-Lithuanian architect, is again somewhat closer to the first subgroup with an average DP value of 2.52 and PLT 1.05. At the end of the Soviet period, the projected Kalniečiai and Šilainiai show the social average DP (0.91 and 0.96) and PLT (0.43 and 0.45) values. The maximum of these indicators is 14.45 and 2.07 respectively. It is interesting, that the PLT indicator is even smaller and more social than the classicist cities, thus reflecting specific urban solutions that seek to form closed inner yard spaces. However, the PE average (~0.04) and the mean MT (~ 0.59) are basically the same as other modernist cities, so the investigation of this subgroup says that it is dynamically well-readable cities with statically readable living quarters spaces and non-readable common use spaces of a higher hierarchical level.
Figure 5 DD of the Modernist cities
As the fifth intermediate transition group, the Renaissance cities have highlighted. Without going into the calculated indicators that are close to the model of the Middle Ages of Western Europe, it is worth paying attention to at least slowly, but increasing DP-normalized maxima of the indicator. This shows the emergence of representative spaces and the increase in their dimensions. The beginning of the specialization of public spaces characterized by Renaissance reflects a lower intensity indicator reaching 0.4 in comparison with the medieval 0.2 (a larger numerical value reflects a lower intensity of use of public spaces). On the other hand, all the investigated cities (Simonetta, Palmanova, Nove Zamky, Zamosc) are very small, and it did not allow to reveal their regular network characteristics, by comparing them with frequent, at least somewhat deregulated, medieval Gothic plan networks through the PLT indicator. In accordance with this precedent, it is worth considering another improvement or supplement to the described methodology – the artificial increase of the small spaces network, in order to better reveal of its nature. On the other hand, this observation also reveals a way to make large, permanent urban structures more readable- to share them with visually perceptible limits, which corresponds to one of Alexander’s models. Indicators that are not significantly different from those of the Middle Ages also fit well with Mumford’s statement, that the Renaissance urbanism shows the moderate roots of those phenomena that are greatly presented only in Baroque and Classicism.
Figure 6 DD of the Renaissance cities
Just like two examples that did not fit any group is Venice (investigated according to the map of 1834) and Berlin 1688 with a new part close to classicism around the Unter den Linden alley axis. The distinction of Venice indicators is determined by the unique city plan, with the spatial structure of the labyrinth type reached on foot, which is more characteristic of Islamic cities and in Berlin, a much larger part of the city is the medieval part of the unchanged plan.
At the end of the review, it’s worth paying attention to Kaunas research. Talking about the medieval cities, the change in the model of Kaunas Old Town has already been mentioned, comparing its situation in 1798 and 1939, which sensitively reflected the expansion and straightening of some of the spaces. Even more interesting changes are visible both in the situation of Old Town and New Town in 1939 compared to 1990. The main change of the Soviet period in these territories, not taking into account some new or expanded streets, is the abolition of quarters of internal land-use borders, related with private land ownership refusal, which made the former private space semi-public or even public. The normalized indicators also are responding to this change, which indicates a substantially changing urban-spatial genotype of the territory and, probably, scenarios used by the city. This, of course, is also related to changes in the experience of the above-mentioned territories, although, at first glance, the structure of the perimeter building, the network of streets and other formal “valuable” features remain unchanged. Some illustrative indicators are:
- In the New Town, average values of DP decrease from 1.64 in 1939. to 0.60 in 1990, showing a decline in the average size of public spaces not typical of the classicist city.
- Correspondingly, the inner structure of the labyrinth type blocks formed by itself increases the mean of MT and PE from 0.93 to 1.14 and from 0.12 to 0.21.
- The intensity of use of public spaces is decreasing very sharp – from 0.24 to 0.55. It testifies to the fact that part of the daily street cultural activity has probably moved from the streets to the inner courtyard, thus living streets expanding into more representative spaces, and so on.
Summarization and the final word
Undoubtedly, further research and development of the model is needed, which includes considerably more subjects investigated, however, the investigation presented in the article allows, at least to state preliminary, that the urban landscape spatial readability model, in essence, helps more complexly to see and understand the city’s space, the regularities of the interaction of its social contents and the specificity of the spatial network.
The proposed normalized model, as shown by the pilot two-stage investigation, well reflects the commonality of both the structures investigated and individual differences and recognizes the major urban genotypes and their peculiarities that have emerged in urban history. More importantly, the readability indicators 4 + 3 not only quantifies the cities but also allows us to perceive the possible generalized spatial usage scenarios (for example, specialized-general, integrated-segregated, connected-separated, near-far, etc.).
The investigation showed that the model reflects different cultural urban genotypes, but normalization was based on the perceptions of social distances inherent to the Western culture human. On the one hand, on the basis of the proposed idea of normalization, any indicator may become the starting point, but the linking of them to a cultural context or perception makes the results more understandable. On the other hand, the proposed model allows adapting the normalization process to other cultural perceptions of the environment, for example, there are data that in Islamic cities, not 3, but 7 or 8 turns are perceived as “near” and so on.
Regarding the model’s applicability, several areas are distinguished:
- The test made by the model allows it to be used as a prediction tool, for example, looking for ways to promote street culture in historic parts of the city by measures of urban design.
- The model makes it possible to evaluate the effectiveness of one or other urban measures and to be not only an identification tool for urban usage scenarios but also a tool for creating them.
- The quantitative characteristics allow talking about the model as the basis for the parameterization.
- The orientation towards the genotype allows a fundamentally different look at the cultural protection of the urban heritage – not based on low useful features, talking about the inevitable evolution of urban structures, in the static “valuable features”, but focusing on determining the limits of certain variations, and the maintenance of the characteristics of the spatial areas promoting the genotype and similar usage scenarios, etc. For example, the model allows evaluating both general changes in structure and the change of the situation of single points in terms of readability. In the first case, it can be used to ensure consistent evolution of the urban structure or to compensate one change by others; in the second case, the readability of certain places or objects should not be reduced or increased if it is relevant to specific objects.
- The sequence of the previous conclusion is also the suitability of the model for the monitoring of urban spatial structures from the point of view of their readability, already mentioned.
- In the presented investigation, several possible ways of adjusting or improving the model have already been revealed, for example, the maximum distance limits are used to calculate normalized values, using on the basis of that the largest distance allowing you to recognize the human figure; detailing the intensity index by calculating it not only for the whole entire territory, but also for its individual parts; the increasing of small structures by highlight some of the less well-known properties, etc.
- More examples and more complex urban structures need to be investigated.
- Some relevant improvements are related to the visual graph modeling: in the investigation, the presented DP indicator is based on the principle of “you see and can move right there”. It is also meaningful to try and the model, “you see, but cannot move there”, which would let to reflect a much larger variety of real urban situations, for example, in a fragmented perimeter building environment where another public space can be seen through the gaps between houses.
*The article presents the research carried out in the framework of a research project funded by the Lithuanian Science Council entitled “Modernization of Lithuanian cities in 1960-1990 and its consequences for Lithuanian urbanism as a complex study of the spatial-social phenomenon “, the contract No. SMOD-17024.
- Alexander Christopher, et al., A Pattern Language: Towns, Buildings, Construction, New York: Oxford University Press, 1977, p. 1167.
- Benjamin Walter, The Arcades Project, Cambridge, Massachusetts, and London: The Belknap Press of Harvard University Press, 1999. p. 545.
- Blumenfeld Hans, The Modern Metropolis: Its Origins, Growth, Characteristics and Planning, Cambridge: MIT Press, 1967.
- Brunyé Tad T., Mahoney Caroline R., Taylor Holly A., „Paths with more turns are perceived as longer: misperceptions with map-based and abstracted path stimuli”, in: Perceptual and Motor Skills, SAGE Journals, 2015, April, 120(2): p. 438–
- Chandler Daniel, Semiotics for Beginners, [interactive], 1999 [viewed in 10-09-2018], http://visual-emory.co.uk/daniel/Documents/S4B/
- Cities in the Pre-Modern Islamic World: The urban impact of religion, state, and society, sud. Bennison Amira K., Gascoigne Alison L., London, and New York: Routledge, Taylor & Francis, 2007, p. 231.
- Cole Michael, Cultural Psychology: A Once and Future Discipline, printed in USA: Harvard University Press, 1998.
- Cullen Gordon, Concise Townscape, London: Routledge, 2015, p. 200.
- Hillier Bill, et al., „Creating Life: Or, Does Architecture Determine Anything?”, in: d‘Architecture et Comportement / Architecture and Behaviour, Lausanne: Ecole polytechnique fédérale de Lausanne, 1987, Nr. 3 (3), p. 233–
- Hillier Bill, et al., „Natural Movement or Configuration and Attraction in Urban Pedestrian Movement“, in: Environment and Planning B: Planning and Design, SAGE Journals, 1993, volume 20, p. 29–
- Hillier Bill, Hanson Julienne, Social Logic of Space, London: Cambridge University Press, 1989, p. 296.
- Hillier Bill, Space is the machine: A configurational theory of architecture, London: Independent Publishing Platform, 2015.
- Kaplan Rachel, Kaplan Stephen, Brown Terry, „Environmental Preference: A Comparison of Four Domains of Predictors“, in: Environment and Behavior, SAGE Journals, September 1989, Vol.21 No.5, p. 509–
- Le Goff Jacques, The Medieval World, London: Collins & Brown, 1997, p. 392.
- Lynch Kevin, The Image of the City, Cambridge MA: MIT Press, 1960, p. 194.
- Mohsenin Mahsan, Sevtsuk Andres, „The impact of street properties on cognitive maps“, in: Journal of Architecture and Urbanism, Taylor & Francis Online, 2013, Volume 37(Issue 4), p. 301–
- Mumford Lewis, The City in History: Its Origins, Its Transformations, and Its Prospects, San Diego New York London: A Harvest Book Harcourt Inc., 1989.
- Ode Åsa, Tveit Mari S., Fry Gary, „Capturing Landscape Visual Character Using Indicators: Touching Base with Landscape Aesthetic Theory“, in: Landscape Research, Taylor & Francis Online, February 2008, Vol. 33, No. 1, p. 89–
- Parker Simon, Urban Theory and the Urban Experience: Encountering the City, London and New York: Routledge Taylor & Francis Group, 2004, p. 15–
- Pellegrino Piere, „Semiotics of Architecture“, in: Encyclopedia of Language & Linguistics, sud. Keith Brown, Oxford: Elsevier, 2006, volume 11, p. 212–
- Peponis John, „Building layouts as cognitive data: purview and purview interface”, in: Cognitive Critique 6, Mineapolis: Center for Cognitive Sciences, University of Minnesota,2012, p. 11–
- Salingaros Nikos A., Mehaffy Michael W., A Theory of Architecture, Sökningen: UMBAU-VERLAG Harald Püschel, 2006.
- Zaleckis Kęstutis, „Role of the green structure in creation of preferred urban environment“, in: Green structure and urban planning: final report of COST action C11, Luxembourg, COST Office, 2005, p. 249–
 Bill Hillier et al., „Creating Life: Or, Does Architecture Determine Anything?”, in: d’Architecture et Comportement /Architecture and Behaviour, Lausanne: Ecole polytechnique fédérale de Lausanne, 1987, No. 3 (3), p. 237.
 Daniel Chandler, Semiotics for Beginners, [interactive], 1999, [seen on 10 09 2018], http://visual-emory.co.uk/daniel/Documents/S4B/
 Michael Cole, Cultural Psychology: A Once and Future Discipline, printed in USA: Harvard University Press, 1998, p. 416.
 Amira K. Bennison, Alison L. Gascoigne (editors), Cities in the Pre-Modern Islamic World: The urban impact of religion, state and society, London and New York: Routledge, Taylor & Francis, 2007, p. 231.
 Jacques Le Goff, The Medieval World, London: Collins & Brown, 1997, p. 392.
 Lewis Mumford, The City in History: Its Origins, Its Transformations, and Its Prospects, San Diego New York London: A Harvest Book Harcourt Inc., 1989, p. 657.
 Simon Parker, Urban Theory and the Urban Experience: Encountering the City, London and New York: Routledge Taylor & Francis Group , 2004. p. 15–19.
 Lewis Mumford, op. cit., p. 657.
 Walter Benjamin, The Arcades Project, Cambridge, Massachusetts, and London: The Belknap Press of Harvard University Press, 1999, p. 545.
 Rachel Kaplan, Stephen Kaplan, Terry Brown, „Environmental Preference: A Comparison of Four Domains of Predictors”, in: Environment and Behavior, SAGE Journals, September 1989, Vol.21 No.5, p. 509–530.
 Åsa Ode, Mari S. Tveit, Gary Fry, „Capturing Landscape Visual Character Using Indicators: Touching Base with Landscape Aesthetic Theory“, in: Landscape Research, Taylor & Francis Online, February 2008, Vol. 33, No. 1, p. 89–117.
 Kevin Lynch, The Image of the City, Cambridge MA: MIT Press, 1960, p. 194.
 Kęstutis Zaleckis, „Role of the green structure in creation of preferred urban environment“, in: Green structure and urban planning: final report of COST action C11, Luxembourg, COST Office, 2005, p. 249–255.
 Gordon Cullen, Concise Townscape, London: Routledge, 2015, p. 200.
 Bill Hillier, Space is the machine: A configurational theory of architecture, London: Independent Publishing Platform, 2015, p. 355.
 Lewis Mumford, op. cit., p. 657.
 Nikos A. Salingaros, Michael W. Mehaffy, A Theory of Architecture, Sökningen: UMBAU-VERLAG Harald Püschel, 2006, p. 278.
 John Peponis, „Building layouts as cognitive data: purview and purview interface”, in: Cognitive Critique 6, Mineapolis: Center for Cognitive Sciences, University of Minnesota,2012, p. 11–52.
 Bill Hillier, Julienne Hanson, Social Logic of Space, London: Cambridge University Press, 1989, p. 296; Tad T. Brunyé, Caroline R. Mahoney, Holly A. Taylor, „Paths with more turns are perceived as longer: misperceptions with map-based and abstracted path stimuli”, in: Perceptual and Motor Skills, SAGE Journals, 2015, April, 120(2): p. 438–61.
 Kęstutis Zaleckas, Aušra Mlinkauskienė, Nijolė Steponaitytė, “The plot, located at Kareivinių g. 9 in Kaunas, which is part of the Kaunas Fortress Artillery Solar Building Complex (unique code of the object in the Register of Cultural Property – 26904), historical research in the territory of the Battalion and determination of the description of the main buildings “. Research work. The sponsor is Juozas Vitkus Engineering Battalion of the Lithuanian Armed Forces. Head Assoc. Prof. Dr. Aušra Mlinkauskienė, KTU, 2016.
 Vaiva Vaitkevičiūtė, “Readability of Architectural Spaces”, Master’s Thesis Final, Managers: Prof. Dr. Kęstutis Zaleckis, Johan de Wachter, KTU, Kaunas, 2018.
 Piere Pellegrino, „Semiotics of Architecture“, in: Keith Brown (Editor-in-Chief), Encyclopedia of Language & Linguistics, sud. Keith Brown, Oxford: Elsevier, 2006, volume 11, p. 212–216.
 Bill Hillier, et al., „Natural Movement or Configuration and Attraction in Urban Pedestrian Movement“, in: Environment and Planning B: Planning and Design, SAGE Journals, 1993, volume 20, p. 29–66.
 Hans Blumenfeld, The Modern Metropolis: Its Origins, Growth, Characteristics and Planning, Cambridge: MIT Press, 1967, p. 377.
 Mahsan Mohsenin, Andres Sevtsuk, „The impact of street properties on cognitive maps“, in: Journal of Architecture and Urbanism, Taylor & Francis Online, 2013, Volume 37(Issue 4), p. 301–309.
 Bill Hillier, Space is the machine: A configurational theory of architecture, London: Independent Publishing Platform, 2015, p. 355.
 Piere Pellegrino, op. cit., p. 212–216.
 Lewis Mumford, op. cit., p. 657.
 Bill Hillier, Space is the machine: A configurational theory of architecture, London: Independent Publishing Platform, 2015, p. 355.
 Nikos A. Salingaros, op. cit., p. 278.
 Alexander Christopher, et al., A Pattern Language: Towns, Buildings, Construction, New York: Oxford University Press, 1977, p. 1167.
 Lewis Mumford, op. cit., p. 657.