The calculated distance (air line) between Songgangdong and Yŏnmu is approximately 26 miles respectively 42 kilometers.
By car or train, the actual journey to Yŏnmu is certainly longer, as only the direct route (as the crow flies) between Songgangdong and Yŏnmu has been calculated here.
Air line (approximately)
42 kilometers
23 nautical miles