And that's good - although fairer if it's only based on the value of the unimproved land, rather than the improvement. We don't want to stop people from demolis

And that's good - although fairer if it's only based on the value of the unimproved land, rather than the improvement. We don't want to stop people from demolishing a slum and building a nice house because the taxes will increase, we want them to discourage owning the slum, leaving it abandoned, and waiting for the land to appreciate in value.