The calculated distance (air line) between Yŏnggwang-ŭp and Ongjin is approximately 183 miles respectively 294 kilometers.
By car or train, the actual journey to Ongjin is certainly longer, as only the direct route (as the crow flies) between Yŏnggwang-ŭp and Ongjin has been calculated here.
Air line (approximately)
294 kilometers
159 nautical miles