10 - REGIONS: TERRITORIES, CATCHMENTS AND VIEWSHEDS

Summary

Introduction: thinking about regions

A GIS can be used to create, represent and analyse many kinds of region. Some regions have an objective reality, at least to the extent that they are widely recognised and have a readily detectable influence on aspects of human behaviour. The most obvious examples of this kind are sociopolitical regions such as the territories of modern nation states. Other regions have an objective reality in another sense: that they are defined by some natural process. A good example of a natural region is the watershed; that is, the area within which all rainfall drains to some specified point in a drainage network. A third kind of region is essentially just analytical in the sense that it is created for a specific short-lived purpose and may never be recognised by anyone other than the analyst. For example, an archaeologist might determine the region containing all land within 100 m of a proposed high-speed railway line in order to identify at-risk archaeological sites, but it is the list of sites and their locations, not the region, that is fed back into the planning process.

Regions are readily represented as polygons in a vector map, or less efficiently as cells coded in such a way as to distinguish between inside and outside a region in a raster map. Where the extent of regions are known in advance of GIS-based analysis, as is often the case with sociopolitical regions, their generation and manipulation within a GIS is mostly an issue of data capture and map query.