L4PSA uses OsmAnd, mobile map viewing & navigation app.
I'm Rinalds (L4PSA), a hobby mapper from Latvia. I grew up in Rēzekne and map the Latgale region, which I know first-hand. I do this in my free time as an enthusiast.
I map nearly everything I come across in Latgale, down to small things like ridges:
points of interest
land use
paths and trails
natural features
buildings
I don't do big-city road infrastructure, since I don't have enough experience with it yet. I also mostly skip addresses, because the Latvian bot keeps them up to date.
How I map
Armchair mapping in JOSM, plus surveying on foot or by mountain bike. I sometimes measure widths and similar details with a laser rangefinder.