Hundreds of Free Geospatial PDF Books from the National Academies Press

Last weekend, Slashdot informed us The National Academies Press are offering all their books, over 4,000 of them, for free in pdf format. With searches, you find plenty of geospatial-related books, for instance:

You can even try more specific terms such as:

It's possible you'll find something related to your own interests in there.