The calculated distance (air line) between Masan and Yangp'yŏng is approximately 167 miles respectively 269 kilometers.
By car or train, the actual journey to Yangp'yŏng is certainly longer, as only the direct route (as the crow flies) between Masan and Yangp'yŏng has been calculated here.
Air line (approximately)
269 kilometers
145 nautical miles