I once looked into building an app which piggybacked on CoMaps/OSMAnd's data (saving the user from having two copies of their maps, and me from having to duplicate the UI to manage them), but found that in modern Android it was basically impossible for even the user to access data/files that "belong" to an app, without rooting the device.
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There are converters between different OSM formats and other formats (Garmin comes to mind). It depends on the target. E.g. here: https://www.mapfileconverter.com/free-gis-conversion-tools
Thanks, but I was interested more in the cross-app communication aspect rather than the data formats ( https://codeberg.org/comaps/comaps/wiki/Content-Provider ).
I once looked into building an app which piggybacked on CoMaps/OSMAnd's data (saving the user from having two copies of their maps, and me from having to duplicate the UI to manage them), but found that in modern Android it was basically impossible for even the user to access data/files that "belong" to an app, without rooting the device.
Thanks for the reminder that ContentProvider is the Android term I couldn't remember when I wrote my other comment here.
And the reminder that I should have added this to my list:
3. A ContentProvider app for OSM map data, so that apps can share the same offline map data.