The calculated distance (air line) between Changyŏn and P’yŏngsŏng is approximately 81 miles respectively 130 kilometers.
By car or train, the actual journey to P’yŏngsŏng is certainly longer, as only the direct route (as the crow flies) between Changyŏn and P’yŏngsŏng has been calculated here.
Air line (approximately)
130 kilometers
70 nautical miles