Projects for Apple platforms usually also use .h, where it could mean anything from C/C++ to Objective-C/C++.
In practice, Clang handles mixed C/C++/Obj-C codebases pretty well and determining the language for a header never really felt like an issue since the API would usually already imply it (declaring a C++ class and/or Obj-C class would require the corresponding language to consume it).
If a C++ header is intended to be consumed from C, adding the usual should alleviate the name mangling issues.
Arguably mapping out cities to this degree across the globe is a ginormous effort, on an order of magnitude more so than what Google Maps etc. currently provide. Thus I don’t think it’s entirely unreasonable to try designing something that operates purely in terms of sensory input (and of course map data where available, those approaches don’t have to be mutually exclusive).