I'm still not 100% clear what you want to make, but it sounds like one of those self guided driving tours? If so, have you checked out apps like GuideAlong or

I'm still not 100% clear what you want to make, but it sounds like one of those self guided driving tours? If so, have you checked out apps like GuideAlong or ShakaGuide? The idea is that you'd download the tour beforehand (just a few MB of audio) and then from there on it's just the GPS doing the work. No cell coverage needed. I just used one of those in a national park last week, where there was no cell coverage. It worked very well and would be more precise and user friendly than FM radio (whose range is harder to gauge than geofencing). Sorry if I still misunderstood. Just spitballing here.