The calculated distance (air line) between Kosan and P’yŏngsŏng is approximately 87 miles respectively 140 kilometers.
By car or train, the actual journey to P’yŏngsŏng is certainly longer, as only the direct route (as the crow flies) between Kosan and P’yŏngsŏng has been calculated here.
Air line (approximately)
140 kilometers
76 nautical miles