In an analysis conducted jointly by Statistics Belgium, Eurostat and Proximus, researchers accessed Belgian mobile phone data (from the major network operator, Proximus) and compared it to results of the 2011 census. The paper produced from this research attempted to find the accuracy of mobile phone data as a measure of resident population density in Belgium. The anonymized and aggregated mobile phone data was obtained from Proximus. For each transaction on Proximus's mobile network, the mobile phone location was located to the level of a cell identity. A heat map was then created showing the number of devices in each area, on the basis of localizations by the mobile network. Data were recorded every 15 minutes for one weekday.