Buffers in GIS

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What are buffers in GIS?  A buffer is a reclassification based on distance:  classification of within/without a given proximity.  Buffering involves measuring distance outward in directions from an object.  Buffering can be done on all three types of vector data: point, line, area.  The resulting buffer is a polygon file.

Most often buffers are measured in uniform distance. For example, creating a 50′ buffer around all rivers.  A buffer based on different distances is called a variable buffer.  For example, the noise level surrounding surround a street network may be based on the traffic load.  Therefore a variable buffer may be used to illustrate the noise level by using a larger distance for high traffic roads and a shorter distance for quieter roads.

variable-buffer

For polygons that are buffered, there are two additional types of buffers.  Bidirectional buffers are polygons that are buffered from the boundary outwards as well as inwards.  Setback buffers are polygons that are only buffered from the boundary inward.

polygon-buffers

Can also buffer a buffer, this is called a doughnut buffer if around a point object initially.

How Big Should a Buffer Be?

The distance a buffer should be around a GIS feature is dependent upon the need.

  • Arbitrary Buffers – Gut feelings
  • Causative Buffers – A priori knowledge
  • Measurable Buffer – E.g. measured value such as a viewshed
  • Mandated Buffers – Predefined values (1000′ ordinance around schools)



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