Today I found out that it’s actually a lot easier to contribute to Open Street Map than I thought. There are some serious gaps in house addresses in my area and I was painstakingly using the built in browser editor in the browser.
But, you can use a FOSS app (available on fdroid) called StreetComplete that makes it a lot easier to help out filling in the gaps in your local map data.
It’s really fun - kind of like Pokémon Go but you are actually making an impact 😁
Pretty sure you can download the maps ahead of time, GPS doesn’t require data, then upload the fixes when you get home.
This is what I do, works great