I’m currently developing an android navigation app that uses OSM map tiles as map data. For the time being it doesn’t appear to be necessary to have an API key to download the tiles.
if I publish it on Google Play, will the app need an API key to keep on using the OSM map tiles?
suppose (I keep dreaming) it becomes a success, is it possible that at a certain point OpenStreetMap (not “GoogleStreetMap” LOL) says “sorry, that’s enough. You’re overcharging our servers. We deny you access”?
You can, of course, download all the OpenStreetMap data that you want, and create whatever map tiles you want, using whatever technology you want, for free, forever, providing that you credit OpenStreetMap as described at https://www.openstreetmap.org/copyright .
If you’re talking about using the standard tiles as shown on openstreetmap.org, I don’t believe there’s an API key option for heavier use. Those tiles are provided mainly as an aid to mappers, and will be cut off if operations detects high usage from somewhere. You may want to look at 3rd-party providers of OSM-based maps; Thunderforest and MapBox come to mind. Typically there’s a “free” amount, then you purchase an API key when your product becomes a success. Many of them use a common addressing format, so your app could easily offer multiple map options with little work on your part.
Have you looked at offline vector maps, eg in MapsForge format? That involves space-efficient map data files for a larger geographic area (a state/province or small country), rendered into tiles on the fly on the mobile device. A different approach.