In a computerized society, the volume of data grows unexpectedly, making their processing time a very difficult task. A priority has become the processing of data in useful information and knowledge. Thus we can say that data mining is a result of technological developments. Interpretation of spatial data has made the subject of research over time, reaching now to have a large variety of instruments and software products for representation and interpretation. What we need to understand beyond the facilities offered by one system or another, proprietary or open source solution, is how they work and interact with spatial data.