The calculated distance (air line) between Chasŏng and P’yŏngsŏng is approximately 158 miles respectively 255 kilometers.
By car or train, the actual journey to P’yŏngsŏng is certainly longer, as only the direct route (as the crow flies) between Chasŏng and P’yŏngsŏng has been calculated here.
Air line (approximately)
255 kilometers
137 nautical miles