The calculated distance (air line) between Koesan and Yangp'yŏng is approximately 50 miles respectively 80 kilometers.
By car or train, the actual journey to Yangp'yŏng is certainly longer, as only the direct route (as the crow flies) between Koesan and Yangp'yŏng has been calculated here.
Air line (approximately)
80 kilometers
43 nautical miles