Web GIS tool for population estimate in the city of Rio de Janeiro
ISBN 978-85-88783-11-9
Authors
1Arueira, L.R.; 2Souza, L.; 3Mandarino, F.
1INSTITUTO PEREIRA PASSOS (CITY OF RIO DE JANEIRO) Email: arueiraipp@gmail.com
2INSTITUTO PEREIRA PASSOS (CITY OF RIO DE JANEIRO) Email: leandrogs86@gmail.com
3INSTITUTO PEREIRA PASSOS (CITY OF RIO DE JANEIRO) Email: felipe.mandarino@rio.rj.gov.br
Abstract
Instituto Pereira Passos (IPP), the municipal department of the City of Rio de Janeiro responsible for its geoinformation system, develops web applications to allow public managers and the general public to have a better knowledge of the city’s characteristics. This web GIS application is intended to do estimative calculations of inhabitants per area of the city, using as input a user provided zone. The ArcGIS software package was used to develop this tool, from the creation of the dataset it reads, a population per pixel raster, to the publication of the map and geoprocessing services. The biggest challenge was to create a population per pixel raster, to which was used as input the polygons of the census tracts of the last demographic census made in Brazil, in 2010, by Brazilian Institute of Geography and Statistics (IBGE). The results show a good quality on the estimative calculation, proved by tests. The web app is available at Pereira Passos Institute website for city information, known as Armazem de Dados (Data Warehouse – www.armazemdedados.rio.rj.gov.br). The ArcGIS platform was used during the whole process, from the database setting by the toolbox to the publication in the web environment. The Zonal Statistics as Table tool, present in the ArcToolbox, is used as the basis for this web map. This tool can calculate several statistical variables on a raster database, to one or more geographic zones defined by the user. Therefore, it’s possible to conclude that with the input data as a raster with a population per pixel (area) information this tool can calculate the population estimate of a certain zone by the sum of the population values of each pixel inside of it. It’s important to have in mind some aspects, like the elimination of empty lands from the calculating process and the pixel’s size, which gives a better performance in terms of estimates accuracy. The first step was to work with the database of the 2010 Census 2010, in the census tract scale (the most disaggregated scale available), aiming to calculate the number of habitants per square meters (m²) occupied by each census tract in the city. To obtain the population per pixel raster the following steps were taken: - Extraction of the urban blocks, corresponding to the population’s effectively occupied area, by the ‘Clip’ tool, eliminating in this way the street’s network; - Elimination of squares, that is, urban blocks without population, with the ‘Erase’ tool; - Elimination of land use classes characterized by no residential occupation: non-urbanized group, mineral exploration, recreational and transportation areas, using the database produced by IPP in 2010, the same year of the Census; - Calculation of the effectively occupied area of each census tract, and then the number of habitants per square meters, by dividing the population from each census tract by the resulting area of the respective tract. - Definition of the better pixel size for the raster, according to precision tests of the estimates and processing speed of the tool; - Through the conversion tool from vector to raster database ‘Polygon to Raster’, was achieved the raster of the population per pixel (3m x 3m = 9 m²). It’s important to highlight that the geographic base of the census tract for 2010 in Rio de Janeiro city was built in a partnership between IBGE and IPP, which allows a large knowledge and trust in this important database, the main source of all this work.
Keywords
people per pixel; population; Rio de Janeiro