[matt4077]

It's a drop in the bucket if you look at the percentage it would add to total available land, and also considering that the ground isn't usually the most expensive part of construction, and that most airports are outside the cities they serve.

One interesting data point in that regard is Berlin's Tempelhof Airport (which you might remember from Indiana Jones 3). It's extremely central because it was one of the first commercial airports and was shut down a few years ago.

It's a park now and will probably remain–the plan to build even a few houses was killed by a referendum. It's also a really fascinating place, because it feels entirely unlike a normal park. There are very few trees, so it's much more open. The runways remain unchanged, and it's quite an experience to jog there, with all the history that place has seen always on your mind. (https://www.google.de/maps/@52.4760745,13.3994616,3a,75y,279...)