The calculated distance (air line) between T’ongch’ŏn-ŭp and Changyŏn is approximately 159 miles respectively 255 kilometers.
By car or train, the actual journey to Changyŏn is certainly longer, as only the direct route (as the crow flies) between T’ongch’ŏn-ŭp and Changyŏn has been calculated here.
Air line (approximately)
255 kilometers
138 nautical miles