The calculated distance (air line) between Changyŏn and Gwangmyeong is approximately 110 miles respectively 178 kilometers.
By car or train, the actual journey to Gwangmyeong is certainly longer, as only the direct route (as the crow flies) between Changyŏn and Gwangmyeong has been calculated here.
Air line (approximately)
178 kilometers
96 nautical miles