All GIS provide the user with tools to calculate spatial properties of entities - the length of a line, the area of a polygon, the maximum and minimum values of a surface etc. The same GIS allow you to perform spatial queries that amongst other things allow you to retrieve information based on spatial position or locate objects that meet specified criteria. These are relatively trivial computations if the database has been designed well and anyone who has used GIS will almost certainly have made these measurements and queries. Having said that we should also appreciate that understanding the results of spatial queries and - as you will discover - spatial analysis in GIS require an understanding of spatial concepts just as much as GIS software. In this topic you will be introduced to some important concepts: the effects of different spatial data models, scale issues, spatial dependency, spatial autocorrelation and the problems caused by modifiable area units.