There's plenty of land in Tokyo, it's just all used for something, not sitting empty, which I would think is the case for any normal city. The zoning laws mean

There's plenty of land in Tokyo, it's just all used for something, not sitting empty, which I would think is the case for any normal city. The zoning laws means that land can be reused, at any time, for housing if some company thinks it's more profitable to build a housing building there than a warehouse or a store. Restrictive zoning means only a portion of the land can be used for housing, and can never be turned into housing as land becomes more valuable. The amount of land is irrelevant. Go back and look at the article, in particular the picture of the NYC zoning map. Only certain portions of the total land is actually usable as housing. In Tokyo, this just isn't the case: almost all of it is. You can't tear down an old warehouse in NYC and build a condo tower there, at least not without a lot of political difficulty. In Tokyo, it's pretty trivial.