The street map is one of the most important instruments of information for planning and implementation of public policies by the local government, since it is necessary for developing urban policies involving spatial location. Furthermore, the street layer is basic for georeferencing of other spatial database information in GIS, such as the addressees map and also for network spatial analysis.
In informal settlements, such as the “favelas” of Rio de Janeiro, there are several obstacles that make street mapping difficult using geospatial technologies, either by remote sensing or by field work using GPS. Among these, we can consider adverse topographic conditions, irregular network of streets and parcels and high density of occupation. For these reasons, these areas lack street information in general. Despite these difficulties, it’s highly necessary to have a street map, due to its importance for meeting the need of public services, implementing of households’ addresses and for health and education programs, among others.
With the objective of improving the quality of existing streets and addressing information in “favelas”, the Municipality of Rio de Janeiro, through its mapping and GIS department, called Instituto Pereira Passos (IPP), started a work to consolidate a more precise and complete streets’ database. Activities developed involved consolidating in one single streets database information of different cartographic sources, including identification in orthophotos, all these information being validated in field by local civil society.
It will present the peculiarities, difficulties and solutions of a methodology for this challenging street mapping, which contributes to improve a GIS-based management of information and policies for the development of informal settlements.
The problems for mapping of streets in informal settlements
The map of streets is essential for locating spatial events in the cities and it is used for both people who live, work and transit in there, and private companies or public institutions that manage its activities based in urban areas. Since a great part of municipal action and policies deal with spatial relationships, street mapping is basic for its strategies and actions addressing the needs of the citizens. For this important matter, IPP – the core of GIS in the Municipality of Rio de Janeiro – is responsible for its management, maintaining the street map of the city.
Nevertheless, the mapping of informal settlements – known as “favelas” in Rio de Janeiro – imposes physical, technological and operational problems to develop city’s GIS databases of these areas. The high density of construction, with few open spaces, and the irregularity in its urban layout bring difficulties to the acquisition of information. Considering the use of remote geotechnologies, orthophotos, satellite or remote sensing imagery, it is required large scale maps (at least 1: 1,000) for a high level of detailed information to cartographic restitution, making it expensive and often impracticable. Field works, like GPS tracking, are complicated too, because of the dense-built environment, which causes distortion and interferes in the precision of coordinates captured in this manner. Even traditional methods, such as measurements and topographic surveying, are troubled because of operational difficulties, for internal displacement in an irregular street network, formed in general by narrow alleys. The “favelas” also are usually placed in terrains of environmental risk, like slopes and flood areas, and a great part of them are dominated by criminal organization of drug dealers, which also represent difficulties for this kind of work.
Due to this combination of factors, digital geographic streets database is characterized by little quantity, with the representation of only wider streets, or even total absence of mapped streets, as it can be seen in figure 1.
Figure 1 – An example of lack of information in the streets database in Rocinha, one of the biggest “favelas” in Rio de Janeiro.
Developing a strategy for “favelas” street mapping
Considering the need to overcome these problems and to provide better information for use by various departments of the Municipality of Rio de Janeiro that conduct actions in these territories, above mentioned IPP started with the challenging task of implementing procedures aiming the production of a reliable and more complete street database of informal settlements. The objective was not only to mitigate deficiencies in municipal cadaster about this layer of information, but also to improve the management of several other information that can be produced by GIS tools – approaching the treatment given to informal and formal areas of the city and putting an end to the historical segregation that once existed.
The first step was to compare the initial vector database with databases from other sources, verifying the streets that weren’t mapped by the municipality to copy and vectorize them. The databases used were a collection of cartographic restitutions from a municipal program called Favela-Bairro (“Favela-Neighborhood”) and the street’s information collected by Instituto Brasileiro de Geografia e Estatistica (IBGE) – the national mapping and census organization – during the activities of Demographic Census of 2010. These vector databases were overlaid with IPP high spatial resolution orthophotos – pixel of 15cm – produced in October/2011, to detect changes in the territory over the other sources of information and new ones, not yet identified. The GIS software used in this work was ESRI’s ArcGIS Desktop 10.0.
The cartography produced under the Favela-Bairro program, although very detailed (scale 1: 1,000), was outdated, but provided useful information. It was delivered in AutoCAD “dwg” format and imported to ArcGIS geodatabase, and the layers of cadastral information, such as edification and street centerlines, besides several street names and toponymy, helped the vectorization of streets not yet available in municipal database, always confirmed with careful observation over the orthophotos, as it is exemplified in figure 2.
Figure 2 – Detail of Santa Marta, “favela” in the area of Botafogo, showing cartographic layer of edification (pink polygons), street names and 2011 orthophoto from IPP.
IBGE’s streets database, produced and used in the realization of 2010’s Census, was a more updated information, not very precise however, demanding analysis about the position of streets in the images for the correct vectorization of streets, to be observed in figure 3.
Figure 3 – Street database from IBGE (blue), over 2011 orthophoto from IPP – Salgueiro hill, neighborhood of Tijuca.
After the accurate work over the streets’ database in GIS, the next step was a validation, essential to ensure the quality of what was mapped, with participation of the local civil society living in these informal settlements. This activity was made by a program that is coordinated by IPP, the UPP Social, with the cooperation of United Nations Human Settlements Programme (UN-Habitat). The UPP Social program is conducted in the “favelas” that area actually occupied by the UPP – Pacifying Policy Units –, a public security action from the government of the State of Rio de Janeiro in some “favelas”, and has the goal to urban, social and economic integration between these territories and the rest of the city, mobilizing different actors involved and articulating policies.
To verify the information, maps were printed and brought to the field, where the population contributing with the program detected in the survey new streets and some corrections to be made in the ones already drawn, besides many street names. Examples of these activities are showed in figure 4.
Figure 4 – Field work for validation of streets’ GIS information: collaboration of local civil society in Salgueiro hill.
GIS and land management
There are many possible uses of the streets map produced, using it combined with other layers of information, both to mapping and to urban planning. Geocoding, distance and route analysis are examples of application of GIS to land management that need this information as input.
Planning, installation and maintenance of public services – street lighting, garbage collection, etc. – and public works – water, waste and sanitation, street paving, accessibility – so necessary in poor areas, all of them need this information to be possible with great efficiency and quality.
Official recognition of the streets in the city’s corporative database of streets, by legal instruments, is a necessary first step to future recognition of land tenure and regularization in currently informal areas, and represents also an application that GIS can help to develop.
The work presented here represents a substantial advance in the representation of the streets in informal settlements, as presented in figure 5.
Figure 5 – Rocinha after the work, with a high density of streets mapped.
This is a primary effort to organization of future information in GIS, both for the collection and use of it. The improvement of the streets map database leads to the improvement of information management, which in turn takes to more efficient public policies in informal settlements. Geospatial technologies consist in important instruments for the representation of territory. Overcome the lack of information by mapping the streets means know better the territory of informal settlements and is a way to promote positive changes by planning and management of the informal settlements of the city.