FactoQGIS : a GUI tool based on an R script to perform Geometric Data Analysis in a Free and Open Source GIS

Abstract

FactoQGIS is an algorithm that allows the implementation of a geometric analysis of multidimensional data in QGIS. More specifically, this tool was designed to easily perform a typological analysis on quantitative data aggregated in spatial units. This method is broadly used in geography but it was up to now executed out of GIS environments, in specific statistical software. FactoQGIS is a tool which precisely fills this gap among GIS functionalities. It first performs a PCA (Principal Component Analysis) and second a HAC (Hierarchical Ascending Classification) on the first factors. FactoQGIS is based on an R script that mainly uses the FactoMineR package developed by Francois Husson et al. (Agrocampus Ouest, Rennes, France). The results (tables and plots) are exported respectively in Excel and png format and then inserted into an html file that automatically pops up in a web browser at the end of the process. The algorithm also creates a new layer with a column indicating the cluster each spatial unit belongs to, so as to make it easy to map the typology. For this purpose, a style file in QML format is generated and can be used as default rendering (the colors of the clusters are the same as those on the 3D hierarchical tree). FactoQGIS is accessible from a graphical user interface directly in the QGIS environment. It will be of particular interest to any user who wishes to simply build and map a multidimensional typology without knowing the R language. To illustrate how FactoQGIS works, we performed a typological analysis on socio-demographic data that are aggregated by “arrondissements” and “communes” in Paris. The R script is available on GitHub .