The calculated distance (air line) between Sangsŏng-ni and Hongwŏn is approximately 82 miles respectively 132 kilometers.
By car or train, the actual journey to Hongwŏn is certainly longer, as only the direct route (as the crow flies) between Sangsŏng-ni and Hongwŏn has been calculated here.
Air line (approximately)
132 kilometers
71 nautical miles