Use OpenStreetMap as background map

[Joel]

OSM layer can be already enabled here, but still with Google API: https://www.lightningmaps.org/?#m=osm

Of course we would use OSM now if we would start from beginning, but 10 years ago Google Maps API was better, free and still has satellite images. However, we will switch to OSM sooner or later. But have in mind, that we can not just get the map tiles from the OSM servers directly as our maps cause 100 million or more tile requests per hour in times with a lot of lightning activity.

great work Tobi 

the thunderstorms generate the visits, not Tobias

By the way, great work