Buffers in GIS

What are buffers in GIS?

Definition of buffer in GIS

A buffer in GIS is a reclassification based on distance: classification of within/without a given proximity.

Buffers and GIS data types

Buffering involves measuring the distance outward in all 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.

Uniform buffer

Most often buffers are measured in uniform distance. For example, creating a 50′ buffer around all rivers or a 100 meter buffer around the points of all cities.

A simple map showing major cities in Oklahoma with a beige circle around each one against a light gray background. — Cities in Oklahoma that have the same distance buffer around them. Map: Caitlin Dempsey.

Variable buffer

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.

In this map below, the cities in Oklahoma have different sized buffers depending on the elevation of that city. The city of Guymon in the northwestern section of Oklahoma has the highest elevation at 952 meters (3,154 feet) and therefore has the largest buffer area.

A gray map of Oklahoma with the point locations of cities buffered in different sized purple circles depending on the elevation. — A variable buffer map of the cities of Oklahoma based on the elevation: the higher the city’s elevation, the larger the circle. Map: Caitlin Dempsey.

Buffer direction in GIS for polygons

Bidirectional buffers in GIS

For polygons that are buffered, there are two additional types of buffers: bi-directional (or bidirectional) and setbacks.

Bidirectional buffers are polygons that are buffered from the boundary outwards as well as inwards.

Setback buffers in GIS

Setback buffers are polygons that are only buffered from the boundary inward.

An example of using setbacks is seen with property lines. Setbacks can be used to buffer the distance from a property line to show how far away from the property line a building has to be.

A diagram showing in green, the difference in buffer direction in GIS. — Bi-directional and setback buffering in GIS. Diagram: Caitlin Dempsey.

In GIS you 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)

Buffering with ArcGIS Pro

This helpful video from Rick Duchscher shows how to use the buffer tool in ArcGIS Pro:

Buffering Tool for ArcMap

If you want to create a zone of equidistance around a geographic feature you will need to understand buffering. Buffering is an important tool for determining the area covered within a specific location. For example, you may buffer school locations to visualize the areas that are within 1000′ feet of a school.

The video below shows how to use the Analysis Tools (part of the Toolbox section) to create a buffer in ArcMap

The video is 1:36 minutes long.

Buffering in QGIS

The Q-tips channel has a two-part video series on how to use buffering in QGIS. Part one:

This article was originally written on June 20, 2013 and has since been updated.