The calculated distance (air line) between Namp’o and Sangsŏng-ni is approximately 85 miles respectively 137 kilometers.
By car or train, the actual journey to Sangsŏng-ni is certainly longer, as only the direct route (as the crow flies) between Namp’o and Sangsŏng-ni has been calculated here.
Air line (approximately)
137 kilometers
74 nautical miles