The calculated distance (air line) between Sejong and Yangp'yŏng is approximately 63 miles respectively 101 kilometers.
By car or train, the actual journey to Yangp'yŏng is certainly longer, as only the direct route (as the crow flies) between Sejong and Yangp'yŏng has been calculated here.
Air line (approximately)
101 kilometers
55 nautical miles