GIS Files 2: Geographical data

2.5: Looking at multiple layers (1)

Combining layers

GIS really gets going as a powerful tool when you start to work with different layers of information about the same geographical area at the same time.

When compiling a conventional map, the cartographer has to draw a balance between displaying as much information as possible to make the map useful without adding so much detail that it becomes cluttered and confusing. With GIS, this problem is removed – many different layers of information can be added, and shown in different combinations and in a different order, depending on the particular message to be conveyed.

Using the power and flexibility of the computer, different data layers can be switched on and off at the click of a mouse, so that many different views can be created for the same location.

The image on the right represents the way in which a GIS can display many different layers of information at the same time. Using different combinations, the display can serve a wide range of purposes that could only otherwise be achieved by producing a whole set of different paper maps. Referring to the graphic:

• Communication network map - creates a communication network map by switching on just the towns, roads and railways
• Relief map - generates a view of the relief of the area by switching on the contours and rivers
• Communication network and relief map - gives a view of all these layers together which can help to analyse the spread of urbanisation in relation to networks and relief.

Vector data can also be shown in combination with Raster data, the latter usually in the form of a backdrop.

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