One common spatial analysis in GIS is to buffer data. Buffers are widely used in various industries, including urban planning, environmental management, transportation, and public health.
So, what are buffers in GIS?
What is a buffer in GIS?
A buffer in GIS is a reclassification based on a specific distance. A buffer in GIS is a defined zone or area created around or within a geographic feature such as a point, line, or polygon.
The buffer is typically measured in units of distance, such as feet, meters, or kilometers, and represents a specific radius or width around the feature. For example, if you create a buffer of 10 meters around a river, you end up with a corridor 20 meters wide (10 meters on each side of the river) that follows the river’s course.
The purpose of creating a buffer is to identify and analyze spatial relationships between features within that distance. Buffers help answer questions like “What are the features within a certain distance from a given point?” or “How many road segments intersect a specific buffer zone?”
Uses of buffers
Buffering is a common analysis in GIS.
Many cities have ordinances that restrict the use of some types of business within the distance of sensitive areas. For example, a city that prohibits the selling of alcohol within 1000 feet of a school will create a 1000′ buffer around each school to show the areas where bars are not allowed to operate.
Buffering can also be used to identify if a geographic feature is found within proximity to another geographic feature. For example, a business may use buffering along with census data to see the demographics of customers that live within a certain distance of their store.
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.
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.
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. Setback buffers are also known as negative buffers as the buffering distance is often set through the use of negative numbers.
The term “negative buffer” might sound contradictory at first, but it’s a useful concept. Instead of expanding outwards from a feature, a negative buffer contracts inward. It effectively shrinks the feature’s area or perimeter. If you apply a negative buffer of 5 meters to a park boundary, the resulting area would be the park’s original area minus a 5-meter-wide strip around its edges.
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.
In GIS you can also buffer a buffer, this is called a doughnut buffer if around a point object initially. A donut buffer, also known as a ring buffer, is created when you make two concentric buffers around a feature but remove the area of the smaller buffer from the larger one. The result is a ring or donut-shaped area that surrounds the feature but does not include the feature itself.
For example, imagine you want to analyze the area within 1 to 2 kilometers from a lake. You would create a buffer of 2 kilometers and another buffer of 1 kilometer around the lake. The donut buffer would be the area between these two buffers, excluding the area within 1 kilometer of the lake.
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.
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Fonte : National Geographic
