> GDP per square metre is probably the best metric, even though it's the more rarely used one. [1] has a neat map of Europe by GDP density.

Well, it would be the best metric, if your country was homogeneously populated.

If everyone lives in one big city and there's literally no one in the rest of the country, then I expect mobile reception (and every other service) to be pretty good for everyone, because they all stay in the big city.

> However Germany is still very high in both GDP per capita and GDP per land area. Roughly on par with the UK, and far higher than France which has a much better mobile network

Yes, France, Germany and UK are all equal enough in these measures (well within an order of magnitude) that the much bigger difference in mobile networks is most likely due to some other factors.

> If everyone lives in one big city and there's literally no one in the rest of the country, then I expect mobile reception (and every other service) to be pretty good for everyone, because they all stay in the big city.

Sometimes the reception is good but the data rate is poor because of too few towers per person, or because the cellphone companies connections to the wider internet are saturated.

Luckily Germany is pretty homogeneously populated. Far more so than the UK (England is pretty even, but Scotland is far emptier) or France (1/5th live in the Paris metro area).