How to Build Geocoded Precinct Boundaries from Address Lists: the Italian Case

Abstract

Electoral results at the national and regional level are today relatively easy to retrieve for many countries thanks to decades of collecting efforts. However, things get complicated when we need to access detailed and granular-level electoral results (such as precinct data). We introduce two novel methodologies to reconstruct the approximate polygons of precincts from voter's address lists that rely on the Voronoi diagram and Census blocks shapefile. Using these methodologies, we build a new Geographic dataset of electoral results for several Italian cities covering the last 20 years (1999-2021) of different types of elections (national, regional, municipal, and referendum). The proposed methodology is scalable to other Italian cities and countries that provide voters' address lists without geographic coordinates, opening the possibility of studying granular geographic data related to electoral results. We also offer a framework to validate the methodologies and show how those perform against an externally hand-drawn dataset. We made the dataset available on a public repository.

Keywords: precinct data, election dataset, italy, GIS