If there were no empty properties, there wouldn't be any squatters. Given that there are apparently a lot squatters (in Spain), we can assume that there are a lot of empty properties.
Many cities have a lot of empty properties. Sometimes because they're derilict (and maybe the owner can't/won't repair); sometimes because it's hard to sell/rent out; or maybe the owner is just obscenely rich to the point of not caring. Whatever the reasons, this is something that shouldn't be allowed to exist. Cities are usually seriously space-constrained (by a river, or ancient walls, or roads etc). Not wasting existing real estate should be a no brainer.
Many cities have a lot of empty properties. Sometimes because they're derilict (and maybe the owner can't/won't repair); sometimes because it's hard to sell/rent out; or maybe the owner is just obscenely rich to the point of not caring. Whatever the reasons, this is something that shouldn't be allowed to exist. Cities are usually seriously space-constrained (by a river, or ancient walls, or roads etc). Not wasting existing real estate should be a no brainer.