In urban planning it is important to assess how well a city is covered by various public services such as hospitals or schools. An effective way to do so is to compute isochrones. An isochrone is a possibly disconnected set of all space points from where a query point is reachable within a given time span.
By joining an isochrone with the inhabitants database, the percentage of citizens living in the isochrone area can be determined. Thus, isochrones support city planners in answering questions such as how many kids can reach a school or kindergarten in 15 times. The computation of isochrones gets more subtle when different modes of transportation are considered, e.g., the use of the public transport system in addition to walking makes isochrones also dependent on the desired arrival time.