The calculated distance (air line) between Sinsang-ni and Changyŏn is approximately 157 miles respectively 253 kilometers.
By car or train, the actual journey to Changyŏn is certainly longer, as only the direct route (as the crow flies) between Sinsang-ni and Changyŏn has been calculated here.
Air line (approximately)
253 kilometers
137 nautical miles