GIS Files 4: Putting it all in a system

4.3: What happens where? - The power of the spatial query (2)

Buffers

It is possible to analyse how close objects are to one another using a buffer. A buffer is a shape based on any other existing object (point, line or area) that can be generated by the GIS. The buffer object represents the total area within a certain distance of a given feature.

Example of point buffer:

• 200m buffer
• 500m buffer

Example of line buffer:

• 200m buffer
• 500m buffer

Example of area buffer:

• 200m buffer
• 500m buffer

You can use the GIS to generate buffer zones and then identify all features that lie within a particular distance. For instance, you can select all addresses within a 500-m buffer of a busy road and compare these with data about the incidence of asthma. By comparing both sets of data you can work out if there are statistically more asthma sufferers living in the buffer region than in the general population. This allows you to analyse whether proximity to a busy road is likely to be a factor in the cause of asthma.

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