Building a collection of reference and academic texts on GIS can be costly. There are some free online source materials that can be a valuable contribution, especially if your book budget is nonexistent. Most of these free GIS books are available in downloadable PDF format and can be read from a computer or on an eBook reader. A few are only available online.
A good starting place for finding GIS books is the The National Academies Press site which offers over 4,000 titles in PDF format for free from its site. For example, a search for the term “GIS” returns over 1,100 results.
The classic book, “Map Projections: A Working Manual“, has scanned by the USGS and made available for free online in both PDF and DjVu formats. The volume was originally published in 1987 and was written by John P. Snyder. The book provides an overview of the “appearance, usage, and history is given together with both forward and inverse equations for each [map] projection.”
This urban planning and GIS book entitled, “GIS in Sustainable Urban Planning and Management” is an open access book focusing on the use of GIS in sustainable urban planning and management includes six chapters containing exercises and GIS data that can be downloaded to learn how to reproduce some of the analyses from the book using QGIS.
The third edition of “Geospatial Analysis – A comprehensive guide” is available for reading online and “covers the full spectrum of analytical techniques that are provided within modern Geographic Information Systems (GIS) and related software products”. The book was written by Michael de Smith and Paul Longley of University College London, and Michael Goodchild from UC Santa Barbara. PDF versions of the book are available for purchase from the site.
Esri offers free eBooks as part of its “Best Practices” series. The booklets over examples of the use of GIS in different industries and subjects in GIS. Select topics include GeoDesign, Essays in Geography and GIS, GIS for Oceans, and Managing GIS. More: These Two ArcGIS Books are Free from Esri
The Rutgers Center on Public Security offers a free PDF version of “GIS for Public Safety: An Annotated Guide to ArcGIS Tools and Procedures“. From the site: “This book, GIS for Public Safety, focuses on Esri’s ArcGIS functionality (the most popular GIS software, worldwide) and presents many of the tools and techniques that are commonly used by public safety researchers, analysts, and practitioners.” The book can also be printed to order for $32 each.