The calculated distance (air line) between Katwijk aan den Rijn and Heerlen is approximately 113 miles respectively 181 kilometers.
By car or train, the actual journey to Heerlen is certainly longer, as only the direct route (as the crow flies) between Katwijk aan den Rijn and Heerlen has been calculated here.
Air line (approximately)
181 kilometers
98 nautical miles