ABSTRACT
As we discussed in Chapter 1, the feature that most clearly distinguishes GIS from other computer systems such as cartographic or drawing software, is the capability to transform spatial data and to use a range of existing spatial data to produce new data themes. This functionality allows users of GIS to model the processes that take place in the real world. It is often said of the spatial database in a GIS that the ‘whole is more than the sum of the parts’. What this rather cryptic statement means is that when using GIS, the individual data themes that were originally entered into a given spatial database can be manipulated in combination to realise new information which was not present (at least not explicitly present) in the original.
