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4.5 Bringing data together to acquire knowledge Manipulating the spatial component of a single layer of data is useful, but the full potential of GIS lies in its ability to integrate data from a variety of layers. At a basic level this merely involves combining layers on-screen to compare patterns. This might be as simple as taking a raster scan of a map and placing a vector layer over the top. The raster layer provides a spatial context for the features in the vector layer. Another option is to lay one vector layer on top of another, for example to compare the pattern of roads with the location of farms to see which farms lie near the major roads. Field boundaries might be a third layer added to this. This approach goes beyond basic mapping, as querying the underlying attribute database allows a detailed understanding of a multi-faceted study area to be developed. In this way an integrated understanding of the problem can be derived from many (possibly highly disparate) sources. Healey and Stamp provide an example of this in their study of regional economic growth in the north eastern United States (Healey and Stamp 2000). They have created a large and comprehensive database that contains industrial plants, such as blast furnaces, foundries and coalmines, represented by points. This is combined with polygon data showing the boundaries of natural resource deposits and, in areas of more detailed study, land parcels. To study the economic development of these they also needed a database of the transport system, and this is reproduced by layers of lines which include the railroad and canal networks, the turnpike roads and the rivers. This can be combined with aggregate, background information, such as that extracted from both the population and industrial censuses. Pearson and Collier use a similar approach in their study of agricultural productivity (Pearson and Collier 1998). As was described in Chapter 2, they combine environmental information in the form of raster grids and terrain models with information from the tithe surveys and census data represented by polygon layers. Siebert brings together information on changing land-use, changing transport systems, administrative units, and population distribution to explore the urban development of Tokyo (Siebert 2000). |
