Jo' in Joetsu City is the same as 'kami' in 'kamigata' (former name for a region of Japan referring to the cities of Kyoto and Osaka); therefore, it indicates that the direction close to Kyoto and in this case, the direction corresponds to the 'southwest.'
上越市の「上」は「上方」（関西の旧称）の「上」と同じく京都に近い方位を意味し、この場合は「南西」にあたる。