Geographic Information Systems: An Introduction, 3rd Edition

14.12 Buffer Zones

Buffer zones are used to define spatial proximity. These comprise one or more polygons of a prescribed extent around points, lines, or areas (Figure 14.20). Using the buffer zone technique, points and lines can be given an appropriate surface representation. The new polygons have the attributes of the original objects, or they can be given new attributes. For each element, coordinates are calculated for the buffer zone limit. The limit will normally be circles around points and parallel lines on each side of the line. In addition, single lines are limited at each end with a half circle. Where there are overlapping buffer zones, these can be merged into one surface. Around periphery lines of surfaces, a single limit can be made at the inside or the outside of the periphery, known as a setback. Many GISs support the automatic compilation of buffer zones. Here, the operator interaction usually consists of keying in specific zone parameters, such as stipulating a 50 m zone width on either side of a road, in order to be able later to determine which objects lie within and, possibly, outside the buffer zone.

The creation of a buffer zone is not in itself an analysis, but the new polygons that are created can be used in analysis. Buffer zone polygons may be processed in the same way as polygons generated during operations such as overlay, arithmetic, logical, and statistical computations in which attribute values come within the respective zones.

Figure 14.20

Buffer ...