A comparison of the results of using ArcGIS and QGIS tools for the generalization of urban base maps
ISBN 978-85-88783-11-9
Authors
1Castro, M.C.; 2Sarot, R.V.; 3Sluter, C.R.; 4Delazari, L.S.
1UFPR Email: castro.monicac@gmail.com
2UFPR Email: rhaissa89@gmail.com
3UFPR Email: robbi@ufpr.br
4UFPR Email: luciene@ufpr.br
Abstract
In accordance with Brazilian laws the official mapping should cover the whole territory at 1:25,000, 1:50,000, 1:100,000 and 1:250,000. Official maps for the urban areas are at 1:2,000 scale and maps at smaller scales are not produced by cartographic generalization which means Brazilian Topographic Maps are only produced by direct survey. Therefore, it is necessary to develop a methodology to produce topographic maps at different scales by cartographic generalization that can be suitable for the diversity of the Brazilian territory. In order to propose this methodology we have studied the generalization tools to simplify and smooth in ArcGIS 10.0 and Quantum GIS Chugiak (2.4), since the algorithms used to develop these generalization tools are supposed to be the same, according to the description of these tools on ArcGIS Resource Center and Documentation QGIS 2.6. Our goal at this moment of our research is to compare the available generalization tools in these GIS software when applied to the following features: buildings, properties limits and streets. A generalization model must rely on the following aspects: the features characteristics, the representation problems, the order of the operators’ application and the tolerance values for every operator and the specific objectives of the map. Thus it is difficult to create a unique generalization model that considers all those aspects and it is also suitable to the whole map. The representation problems and the relationships between features are aspects that define which operators must be apply and in what order. The order in which the tools should be applied is simplification (for area and line features), smoothing (line features) and amalgamation (area features), also known as aggregate polygons in ArcGIS and union in QGIS. The tools were applied when representation problems, such as congestion and coalescence, were detected. The tolerance values used to apply these operators are based on the minimum values indicated in [1] and [2]. The proposed methodology include 6 steps: (1) identification of the representation problems on the map when the scale is reduced, and (2) selection of the suitable tools to solve those problems, (3) setting of the tolerance values, such as minimum distance between points, (4) application of the generalization tools, (5) comparison of the results in the generalized features. The results were analyzed according to the amount of common points eliminated, line length and sinuosity, area and perimeter of the area features, changes in features characteristics, visual quality (graphical overlay) and size of the resulting files. These aspects should provide better results when we compare automated generalization with the manual procedure. This information could help the user to choose the appropriate tool in a project in order to improve the result in the generalization process. [1] TAURA, T.A. Estudo da Simbologia para Cartas nas Escalas 1:2.000, 1:5.000 e 1:10.000 de Mapeamento Urbano do PARANACIDADE e Generalização Cartográfica. 93 p. Dissertação (Mestrado em Ciências Geodésicas) – Universidade Federal do Paraná. Curitiba, 2007. [2] SWISS SOCIETY OF CARTOGRAPHY. Maps Graphics and Generalisation. Cartographic Publication Series no 17, 2002.