How? The area west of 280 is mostly protected land, so it's hard to build. Some of the empty areas out by Alviso/Milpitas are superfund sites. Apparently it's much harder than it looks to reclaim the Bay and build on it (best chance of opening up large amounts of land). Is there some map that shows areas that can be developed?

Also, Santa Clara county is chock-full of EPA superfund sites. Lots of soil and groundwater contamination.

Well, the "protected land" is one of the biggest political constraints.

The other is that most of the built land is zoned extremely low density.