I am about to develop my first Android app (so I am a newbie in mobile app development). For this I will need OSM data of the whole globe, but only data with tags highway, boundary, waterway and natural (here only water bodies). This data I will download (still need to figure out how I can download such a big data set, Overpass API??) and later style it in my own way in QGIS. The map I would like to use as a base map in my offline app.
Now I know that I can use map tiles to render the data faster in a map viewer. However, I still have some problems understanding why and how it is possible to use so much data in an app when the data storage restrictions of apps are a few MB's. The map tiles would still use the whole OSM data I downloaded, which is several GB's, isn't it?