Stephen Wise has been a regular contributor to GeoEurope and his 'Back to Basics' articles have provided a clear and simple introduction to the inner workings of Geographical Information Systems (GIS) for a non-specialist audience. He now presents the original articles with new material and provides a new coverage of both major types of GIS: vector and raster systems. Undergraduates and professionals should get a better understanding of how GIS operate in the way that they do, such as how spatial data is stored on a computer, how the different methods affect the capabilities of the GIS, how basic operations performed and how the choice of algorithm affects the speed of the system.