Parliamentary elections were held in Finland in April 2019 and to better visualize the results, I went on a quest to generate polygons for each of the 1937 voting districts. Voting district polygons are not open data except for few major cities, but address points for buildings are open data in Finland and they also have information about which voting district each address belongs to. The talk aims to give examples and tips of how to work with bigger datasets with OSGeo tools and how to deal with errors and uncertainties in your data analysis.