The calculated distance (air line) between Ouderkerk aan de Amstel and Purmerend is approximately 15 miles respectively 24 kilometers.
By car or train, the actual journey to Purmerend is certainly longer, as only the direct route (as the crow flies) between Ouderkerk aan de Amstel and Purmerend has been calculated here.
Air line (approximately)
24 kilometers
13 nautical miles