[andy]

I saw something like this a few weeks ago, maybe this actual site or one fairly similar.

I'm not sure what it tells us about actual coverage strength. It seems to me that it is based more on a slightly different version of probability, namely the positions of the phones connected to the application rather than the actual signal strength they are experiencing. And many of those phones are in vehicles on main roads.

If I search where I live, it shows something in my village, but a bit weaker out to the edge where I am.

They declare an order of network strength for my house (2g, 3g, 4g all selected; no 4g here though)

1. Vodafone
2. O2
3. EE (T-mob & Orange)
... and Three is not even mentioned

The order I would tell you is
1. Three
2. T-mobile 3g
3. Orange 2g
4. O2 2g
5. Orange 3g
6. T-mobile 2g
7. Vodafone only present about half the time, 2g or 3g about equally
8. O2 3g never (it was fairly good but removed about 5.5 years ago)

simplifying that to their format:

1. Three
2. EE
3. O2

in other words completely the reverse order, and they omitted the best signal here

If I switch to their Towers tab, the nearest 4 x O2 to me are in fictitious places, including in the river quarter of a mile south of here. I suspect they may have a similar algorithm to Google Maps for guessing site locations, but less effective, though other areas look more accurate.