E.g. England that invented it having a really high density or Eastern Germany being basically blank (main tennis hype has been in the 80's in Western Germany).
Tennis is not very popular anywhere. If we use the number of top players each region has as proxy for how popular tennis is relatively, then it's not doing that bad in eastern Europe.
This map would actually be interesting if it were normalized against population density. Tennis court density per 1000 inhabitants. Probably need to do it per 100.
I think the population density argument plays best here. I'm not as well versed in Spain, but for Portugal the largest concentration is Porto and Lisbon.
E.g. England that invented it having a really high density or Eastern Germany being basically blank (main tennis hype has been in the 80's in Western Germany).