The most important function of GIS is to enable the analysis of the spatial data and their attributes for decision support.
Spatial analysis is done to answer questions about the real world including the present situation of specific areas and features, the change in situation, the trends, the evaluation of capability or possibility using overlay technique and/or modeling and prediction. Therefore spatial analysis ranges from simple arithmetic and logical operation to complicated model analysis.Spatial analysis is categorized as follows.
Query: retrieval of attribute data without altering the existing data by means of arithmetic and logical operations.
Reclassification: reclassification of attribute data by dissolving a part of the boundaries and merging into new reclassified polygons.
Coverage Rebuilding: rebuilding of the spatial data and the topology by "update", "erase", "clip", "split", "join" or "append".
Overlay: Overlaying of more than two layers, including rebuilding topology of themerged points, lines and polygons and operations on the merged attributes for suitability study, risk management and potential evaluation.
Connectivity Analysis: analysis of connectivity between points, lines and polygon in terms of distance, area, travel time, optimum paths etc. Proximity analysis by buffering, seek analysis of optimum paths, network analysis, etc. are included.
Figure 4.1 shows examples of spatial analysis.