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