The calculated distance (air line) between Seoul and P’yŏngsŏng is approximately 131 miles respectively 210 kilometers.
By car or train, the actual journey to P’yŏngsŏng is certainly longer, as only the direct route (as the crow flies) between Seoul and P’yŏngsŏng has been calculated here.
Air line (approximately)
210 kilometers
113 nautical miles