Just looking for a bit of clarification. If I build municipal airports, do they connect cities across the region when those cities are not connected by rail or road?
The municipal airport provides limited functionality when connecting cities. It does not allow the exchange of utilities such as power, water, and sewage because those agents move via road. It also does not allow you to share city services, as those need to travel along roads. It will however, allow workers, shoppers, and tourists to move between cities. It will also ship Freight between cities.
It will raise the happiness of any industrial buildings in proximity, but make any residents nearby unhappy presumably due to noise.
It can be expanded to generate more tourists and higher wealth tourists as well, in fact, adding a municipal airport (or the international airport great work)seems to be the single best way to increase high income tourist traffic.