From my observations it also seems to vary a lot depending on how the person recording behaves. Some people just walk around logging reading along the way. Others go out of the way to find interesting above background level radioactive objects and place the measurement equipment right next to those. Like finding 2 pieces of granite having 6x the background level in a giant pile of other rocks.

Another interesting pattern I saw while browsing around was increased level next to every fancy cast iron light fixture along a specific bridge. The bridge was made mid 20th century so I don't think they are old enough to have used thorium gas light mantles.

Yeah, and I was hoping that you could still look at high-level averaging over a country ("maybe the bad data will average out") but when I looked at a few hotspots it appears that those all came down to a couple uncalibrated-looking devices.

Not very useful or interesting in its current form, unfortunately.

Yeah I checked some tracks and it basically looked like the longer someone spent in a place, the higher the readings got. Maybe when the device doesn't get a lot of ventilation it starts to misread.

Pretty much, there are no shortage of ways to merge such data badly.

Many devices, uncalibrated and drifting, poor time normalisation to address counts accumulating when lingering, ... ffs they probably don't even adjust for cosmic or radon ...

( TBF the last two are pretty picky objections unless you're going hardcore geophysical professional )