Considering the examples above, here are cases where I think the changes could improve existing guides:
Teotihuacan: the archeological site borders municipalities like San Francisco Mazapa and San Juan, each of which has a guide. Since they’re all in the same state, and the tourism is anchored on the archaeological site, a single guide might make sense.
Giant’s Causeway in Northern Ireland, for a somewhat isolated, very popular natural feature.
Maybe the Everglades national park?
For USA cities, Miami area for starters, currently divided in separate guides for Miami, Miami Beach and North Miami Beach, among others.
Greater Los Angeles, San Francisco Bay, Dallas-Fort Worth, etc.