The calculated distance (air line) between P’yŏngsŏng and Ongjin is approximately 95 miles respectively 152 kilometers.
By car or train, the actual journey to Ongjin is certainly longer, as only the direct route (as the crow flies) between P’yŏngsŏng and Ongjin has been calculated here.
Air line (approximately)
152 kilometers
82 nautical miles