The calculated distance (air line) between Ouderkerk aan de Amstel and Heerlen is approximately 108 miles respectively 174 kilometers.
By car or train, the actual journey to Heerlen is certainly longer, as only the direct route (as the crow flies) between Ouderkerk aan de Amstel and Heerlen has been calculated here.
Air line (approximately)
174 kilometers
94 nautical miles