The ESA has its launchpad in French Guiana. It's not only close to the equator but also has a lot of water to the east, meaning that boosters can fall down without hurting people (probably).
But in the Mediterranean Sea, there's quite a lot of water to the east, too. Why didn't the ESA set up their launchpad somewhere around Alicante in Spain such that they don't hit Formentera, Sardegna, or Sicily? The first thing they could hit would be mainland Italy. There's quite some distance to mainland Italy.
The US seem just fine with having their launchpad on their mainland where all their scientists are anyways and where they can supply materials easily, even though it's pretty far away from the equator. They don't ship their stuff down to like Jarvis Island which almost sits on the equator and has a lot of water to the east (and to the west, too, if someone wants to send a satellite up the other way, again, for a change).
Question: What is the (size and shape of the) area you need to be uninhabited for a typical launch?