Analysis of a high sub-centrality of peripheral areas at the global urban context Adriana Dantas Nogueira Universidade Federal de Sergipe, Brazil adriananogueira02@hotmail.com Abstract This paper presents spatio-syntactic analysis of the recent urban configuration of Aracaju (2003), capital of Sergipe (Northern region of Brazil). The most segregated areas were detached from the whole city and they were analysed as sub-centres which can survive with a minimal connection with the main integrated core, the live centre. The hypothesis is that the main responsible factor for that independent status is its inner urban configuration, which has been designed by the mayor planning department as a quasi-grid form, besides it, the existing movement around (interurban one) is much more intense then the movement to (periphery-centre), which was detected by observations in loco and by quantifying data about their vehicular flows. Five most segregated neighbourhoods were analysed essentially regarding their local integration, intelligibility and synergy values, when compared with global integration they have showed lower measures. In this context, long lines have not worked as growth structured elements, as it has happened in other cities around the world, but as a sort of movement around receptors, avoiding be contributors of the high flows in the central area. Significant commercial and institutional activities were almost always found in the most integrated areas, as in the centre and around integrated lines, involving a higher movement. Each neighbourhood lives as a little village, with their own small commercial and institutional activities, although without a great potential of services or working areas. In the recent period, it has been said that Aracaju is a large city because of its link with these mentioned peripheral neighbourhoods. It could be a true statement from many different points of view, but it could be much precipitated to conclude about that, especially regarding the spatio-syntactic results. It could be observed that they are unintelligible peripheral areas and there is a strong sub-centrality happening in each one of them. 1. Introduction: Aracaju and its configurational aspects Aracaju has been designed since its origin in 1855 as a kind of orthogonal and regular grid, but its growth has been very slow until 60s, when there was a good development resulting from the oil discover in its coast and also from a federal politic of general development. Only in the recent past, around 90s, the city has had several urban order problems, which government and private agents have been intervened causing a faster sprawling without basic infrastructure and urban facilities. The city has a specific delimitation of its limits, which has caused a conurbation with other two cities (Sao Cristovao and Socorro), especially because of its peripheral areas, which have been expelled to out of its frontiers. It has an approximated population of five hundred thousand people, but if it can count all peripheral areas, it can reach around eight hundred thousand, what makes possible for being nominated as the Great Aracaju
246 Adriana Dantas Nogueira Table 9: Urban Form Index for the Great Aracaju. Source: by the author Period Urban area (m 2 ) Circle area (m 2 ) Urban Form Index 1890 829.120 2.437.690 0,34 1941 2.002.455 7.194.039 0,28 1949 9.377.756 17.002.484 0,55 1960 16.032.368 27.502.346 0,58 1980 33.385.856 153.444.968 0,22 1988 48.201.654 224.220.724 0,21 1995 90.290.401 690.814.041 0,13 2003 135.788.539 906.582.390 0,15 Figure 109: Urban growth of Aracaju and its urban form index (1890 to 2003). Source: by the author. because of its size and high economic development. Its spatial configuration has been analysed from its urban form index, what brings a very interesting point of view about its linear growth despite of its orthogonal urban grid. The urban form index is calculated from the urban built area that is circumscribed in a circle which involves all of it. It must be between zero and one, the first shows a radio-concentric urban form and the latter a more linear urban form (Table 9 and Figure 109). The most linear configuration can be revealed in its earlier period (1890 map) and its recent ones, starting in 80s to 2003. After 60s, there was a discontinuity in its spatial configuration, when the urban form index changed from 0,58 (1960) to 0,22 (1980). It demonstrates that the new government habitation politic was responsible for implementation of several popular habitation sets, but also promoted many empty spaces between them and long distances to the public and private transport. It can be said that Aracaju became a very fragmented city with a bad accessibility and segregated urban blocks.
Analysis of a high sub-centrality of peripheral areas at the global urban context 247 Table 10: Spatial-syntactic measures from 1890 to 2003 to Great Aracaju Source: by the author. Period axial intellig. synergy Mean Mean local Mean Most lines connect global integr. depth integrated Integration via 1890 29 0.79 0.83 5.52 2.39 2.89 2.37 Itabaiana St. 1941 60 0.77 0.87 5.26 2.13 2.79 2.71 Itabaiana St. 1949 418 0.46 0.67 5.43 1.66 2.81 3.59 Itabaiana St. 1960 866 0.26 0.45 5.3 1.33 2.8 5.28 Itabaiana St. 1980 1963 0.12 0.25 4.80 0.95 2.61 7.38 Br.Maruim Av. 1988 2856 0.1 0.18 4.38 0.69 2.46 9.96 Br.Maruim Av. 1995 5520 0.1 0.19 4.05 0.53 2.30 14.22 Br.Maruim Av. 2003 7562 0.05 0.09 4.34 0.47 2.45 15.77 T.Neves Av. 2. Aracaju and its spatio-syntactic values In recent period of Aracaju, it can be found a potential local movement in its segregated urban blocks, which was verified through observation in loco, counting the vehicular flows at the main avenues and streets, and also through the spatio-syntactic measures (Table 10) measured of each period of its growth. Synergy (which relates global and local integration) and intelligibility (relating connectivity and global integration) present decrease as the city grows, while the main depth increases, the connectivity decreases as well. It means that Aracaju has presented an increased value of depth spaces, at the same time it becomes more unintelligible, what evokes a smaller interaction between its citizens and its configuration itself. Global integration has decreased as the city grows while local integration has continued almost with the same value, besides a little decrease. In 1890, the city had approximately 16 thousand inhabitants and its spatial culture could be defined as an axial and simple geometric structure with axial lines acting as connectors between the downtown and the limits of the city. Its urban grid was orthogonal and its most longitudinal movement occurred at Itabaiana Street, which has obtained the highest global integration value, what becomes like this in the next three analysed axial maps, i.e., 1941, 1949 and 1960 periods (Figure 110). Interesting is to compare its historical data with the highest global integration for the earlier periods, because three of the four existing schools were located in Itabaiana street. Its intelligibility has presented a high value what means a good spatial orientation to the local people. In 1949 map, it can be found schools and cinema and also two of the five bus routes located at Itabaiana Street. New neighbourhoods were implemented, but its urban grid had maintained a compact form and long lines had not the structure function, because the movement around was reinforced by its urban regular grid. At 70s and 80s, there were many important facts and factors which have interfered at Aracaju growth. One of them was the oil discovered at its coast, what has brought a good improvement at local economy and urban development. At 1980 axial map, it can be found a more fragmented configuration, besides its urban orthogonal grid maintenance with some small variations on a sort of quasi-grid and some urban branches with a bad accessibility, what brings a suggestion of a existence of a
248 Adriana Dantas Nogueira Figure 110: Global Integration maps to 1890, 1941, 1949 and 1960 periods. Source: by the author. small kind of movement to (down town- periphery). It can be registered some differences between areas to where rich people were installed and poor people were located, enforcing the speculator process of soil as a good market. There were also big differences at government improvements, facilities and accessibilities, with privileges to the rich social class. The central area has been the most integrated one and maintains a very compact form and a spatial orthogonal configuration. The most integrated street has changed for the first time in decades from Itabaiana to Br. Maruim Avenue (it will continue like this for the next decades as it can be seen at 1980, 1988 and 1995 periods) (Figure 111). At 90s, two different urban processes have occurred: a) increase buildings near the commercial areas and infrastructure facilities; b) urban sprawling, outside the Aracaju official limits. It can be found many urban empty areas, what promotes an increase of the fragmentation as well. The central area continues to be a place of commercial activities. The rich social classes can be found essentially at the south areas and poor people live at the north one, both are involved with spatial segregation. From now, it can be observed a beginning of a stronger sub-centrality, especially in its peripheral areas, outside from the limits of the city. There can be found new commercial areas on them, what promotes a new kind of movement around. 3. Aracaju and its recent occupation Analysing the spatial culture, long axial lines work as flow distributors and not as growth structure. Short lines reinforce the movement around and they represent 97% of all lines. As result, the most of the lines distributes movement around the neighbourhoods, maximizing the sub-centrality while they become isolated because of its own grid characteristic and bad accessibility. The most integrated line was T. Neves Avenue for 2003 axial map (Figure 112). There is a mixture of institutional and commercial activities along this avenue. The city continues its growth like an ortoghonal grid and some quasi-grid, besides its linear configuration if it considers the whole built environment.
Analysis of a high sub-centrality of peripheral areas at the global urban context 249 Figure 111: Global Integration maps for 1980, 1988 and 1995 periods. Source: by the author.
250 Adriana Dantas Nogueira Figure 112: Global integration map of Aracaju, 2003 period. Source: by the author. If the five most segregated areas were detached from the whole city, it could be easier to conclude that they have the smallest global integration values These five areas (Figure 113) were chosen because of their minimal global integration values and all of them have around 700 axial lines (it was not considered the distance to centre or square meters): Sample 1: located at the north of the city, it has a unique access over a bridge. There are residential and industrial activities; Sample 2: located at the northwest area, it is basically a residential area; Sample 3: a western area with residential and institutional functions (federal university campus); Sample 4: a residential southwest area promoted by the government; Sample 5: A rich residential and recreational area of beach houses, which is located along the south coast. Connectivity and global integration values of each detached sample have showed the smallest values if they are compared with the whole system. An area can be defined as unintelligible if its coefficient is higher than the global result. As it can be seen in Aracaju, all of these samples have this character, what means that the human perception of globallocal relation is very weak for the local people. The highest depth values were found in the sample 5, and then sample 4 and sample 1. Other interesting observation is that the sample 5 has not demonstrated a gradual permeability, i.e., there are some high spatial
Analysis of a high sub-centrality of peripheral areas at the global urban context 251 Figure 113: Most segregated areas of Aracaju (samples 1, 2, 3, 4 and 5). Source: by the author.
252 Adriana Dantas Nogueira Table 11: Spatio-syntactic values for the samples and for the whole system (2003 period) Source: by the author. Sample Intelligibility Synergy Mean Local Mean depth connectivity integration 1 0.01 0.06 4.44 2.55 19.4 2 0.03 0.008 5.37 2.91 12.83 3 0.03 0.07 4.33 2.48 16.45 4 0.01 0.03 3.88 2.28 28.8 5 0.0004 0.009 2.84 1.74 29.5 Whole urban system (2003 0.05 0.09 4.32 2.44 16.31 period) values (for example red lines which is more integrated one) e many small values (blue lines), while intermediate values (as orange and yellow lines) almost do not exist. Regarding the specific spatial configuration mentioned and its spatial culture promoting a sort of movement around, the spatio-syntactic measures (Table 11) for the samples can demonstrate that there is a sub-centrality on each one of them. Each sub-centre has worked as a small village which remains alive their functions, as residential, commercial and institutional ones. Trying to obtain a much more specific relation between the samples and the global system, spatio-syntactic values for each detached sample were compared with their values at the urban context (as the city as a whole), looking for differences in the spatio-syntactic measures which could determine other thoughts about their sub-centralities and movements (Figure 114). Local integration values for the detached samples present few axial lines responsible for the highest values. These lines maintain a close relation to commercial activities and bus routes, what can be observed in loco, what is promoting a great movement of people on them. Besides it, the smallest intelligibility values were found on these areas, what means that their inhabitants live at a local level, i.e., they have difficulties to interact with the city as a whole. As result from the comparison, it can be said that the behaviour of both situations is very similar. In general terms, it can be said that all analysed samples are demonstrating that the spatial properties maintain their specificities as detached ones and at the global context as well. The spatial configuration of Aracaju has contribute to the origin of sub-centres, which are maintained through local movement at each one of the samples, as it can be observed through local integration and connectivity values. Centrality was reinforced by the spatial configuration at the live centre of the city with its convex and orthogonal urban grid, where the urban facilities (commercial activities, infrastructure, public transport, and so on) were promoted and where the highest accessibility, intelligibility and integration values were found. Spatial fragmentation was observed essentially from 60s to now, happening to all social classes. Although, at the recent period, there are a increase of the urban sprawling, creating many empty areas and expelling its inhabitants much more to peripheral areas, which have become many small villages far away from the whole city, producing their own and
Analysis of a high sub-centrality of peripheral areas at the global urban context 253 Figure 114: Spatio-syntactic values for the five samples (detached and at the whole context). Source: by the author. independent urban context, as it can be called of sub-centrality. 4. Final Considerations In its urban configuration, long lines have not worked as growth structured factors, as it has happened in other cities around the world, but as a sort of movement around receptors, avoiding high flows in the central area. Commercial and institutional activities were found in the most integrated areas, involving a higher movement. In the recent period, Aracaju has been analysed as an urban complex linked to other nearest urban districts; it could be observed that there are many unintelligible peripheral areas and the urban fragmentation has been increased as well as the socio-spatial segregation. Sub-centrality is reinforced through the continuous linearity of the whole spatial urban form, as could be seen at the demonstrated urban form index. It could be predictable a tendency to fill the empty spaces, what could contribute to increase the urban form index, reaching a much more compact form, as it used to be at earlier periods. Although, the spatial culture of Aracaju has created many peripheral areas which have their own life, working outside its limits with a bad accessibility to the centre, reinforcing the urban blocks (samples) and the movement around. Then it could be maintained like this for a long time. Literature Hillier, Bill. (2000) Centrality as a process: accounting for attraction inequalities in deformed grids. Urban Design International, 3/ 4, p. 107-127. Hillier, Bill and Hanson, Julienne. (1984) The Social Logic of Space, Cambridge, Cambridge University Press. Hillier, Bill and Netto, Vinicius. (2001) Society seen through the prism of Space, In: Proceedings III Space Syntax Symposium, Atlanta, p. 13.1-13.2. Hillier, Bill. (1996) Space is the Machine, Cambridge University Press. Kim, Young Ook. (2001) The Role of Spatial Configuration in Spatial Cognition, In: Proceedings III Space Syntax Symposium, Atlanta, p. 49.1-49-21. Trama Urbanismo. (1995) Cadernos de diagnostico do Plano Diretor de Aracaju, Aracaju, Prefeitura Municipal.