Rita Nicolau
Researcher
Directorate General for Territorial Development
Portugal

Biography
Rita Nicolau has a graduation and a PhD in Environmental Engineering and a masters’ degree in Operations Research and Systems Engineering. Her knowledge on GIS resulted from her participation in several research projects that involved the integration, analysis and modelling of spatial data, applied to environmental, social or health problems. Presently working at the Division for Cities Policy of the General Directorate for Territory Development, her research concerns urban systems.

Abstract
Urban Settlements Delimitation Using a Gridded Spatial Support

Co-Authors:
Elisa Vilares, Head of Division of Urban Policy, DGT - Directo-Geral do Territorio
Critina Cavaco, Deputy Director General, DGT - Directo-Geral do Territorio
Ana Santos, Dr., INE - Statistics Portugal
Mario Lucas, Dr., INE - Statistics Portugal

The identification of settlements that make up urban systems is essential to spatial planning. Although a general consensus on the definition of urban settlements does not exist, the delimitation of these areas is usually performed using morphological and functional criteria, such as population, employment and commuting. The definition of a city and its commuting zone, lately adopted by OECD and the European Commission (OECD-EC), relies on the spatial allocation of the population to 1 square Km grid cells. The allocation of specific variables to grid cells offers the chance to study phenomena which spatial distribution is independent of administrative boundaries, such as urbanization. Because OECD-EC definition leaves out cities below 50.000 inhabitants (small and medium sized towns), these were recently studied in ESPON project TOWN, that proposed a method based on morphological criteria for its identification. According to TOWN, urban settlements are clusters of 1 square Km grid cells with specific population thresholds. As the settlement size becomes smaller TOWN's method becomes problematic. TOWN's team suggests that the allocation of population to higher resolution grid cells and the integration of land cover data can improve settlements' identification. As the Portuguese urban system is mainly composed by very small sized towns, none of the aforementioned methods allows its study. Using an alternative approach we estimate that 98% of Portuguese settlements do have less than 5.000 inhabitants. The approach developed by our team for identifying urban settlements starts by classifying elementary spatial units based on the following criteria: land cover, land use established by municipal master plans, population density and built-up density. Afterwards, contiguous spatial units that present similar classification are merged. Our approach was already tested using two distinct spatial supports: census tracks and 1 square Km grid cells. While the irregular shape of census tracks hampers the delimitation of settlements, the coarse resolution of the 1 square Km grid hinders the identification of very small sized settlements. Therefore our presentation will focus on the results of an essay of the same approach using a 250 square meter grid as spatial support.