Using an isopleth map to determine the population of any area

The aim of this article is to present and verify a method of estimating population numbers based on an isopleth map that meets the volumetric condition. This boils down to a situation where the volume of a solid enclosed by a statistical surface corresponds to the number of people living in that area. To verify this method, an isopleth map of population density was created based on census data from the Central Statistical Office (in Polish: Główny Urząd Statystyczny, GUS) from 2021, referenced to a grid of 1×1 km squares. Population estimates were made for municipalities in the Lublin Province and then compared with the actual population recorded in these municipalities. The results of the comparison showed that the MPE (mean percentage error) was -2.69 and the MAPE (mean absolute percentage error) was 4.2%. As a result, the proposed method can be considered an effective tool for estimating the population in areas for which no systematic statistical surveys are conducted. These may be, for example, protected areas (national parks, landscape parks) or physiographic units. The method is so versatile that it allows working with official data and data contained in global grid models of population distribution.