Heerlen is a city and a municipality in the southeast of the Netherlands. It is the third largest settlement proper in the province of Limburg. Measured as municipality, it is the fourth municipality in the province of Limburg. Heerlen forms part of the city-region of Parkstad Limburg, an agglomeration with about 250,000 inhabitants and encompassing 8 municipalities. It is to the east of Maastricht and north of the German city of Aachen.