There's a crossover between concepts here.
Initially when the world begins there are no player towns with hotels for people to rest in. So the game has a "founding town" near the east edge of each of the eastern regions. They show up on the minimap as the same grey as ghost towns but cannot be taken over or used for anything except staying in the hotel. Once player towns have opened and built their first hotels they no longer serve any purpose but remain on the map.
Normal ghost towns are player built towns that have been abandoned. They show their point score, with 500 being a basic town with no extra buildings. If you choose to take over a ghost town it costs the same as founding a town normally but you get to keep any building work that was already done by the former occupants.