In
geographic information system
A geographic information system (GIS) is a type of database containing Geographic data and information, geographic data (that is, descriptions of phenomena for which location is relevant), combined with Geographic information system software, sof ...
s (GIS) and
spatial analysis
Spatial analysis or spatial statistics includes any of the formal techniques which studies entities using their topological, geometric, or geographic properties. Spatial analysis includes a variety of techniques, many still in their early deve ...
, buffer analysis is the determination of a
zone
Zone or The Zone may refer to:
Places Climate and altitude zones
* Death zone (originally the lethal zone), altitudes above a certain point where the amount of oxygen is insufficient to sustain human life for an extended time span
* Frigid zone, ...
around a
geographic feature
A feature (also called an object or entity), in the context of geography and geographic information science, is a discrete phenomenon that exists at a location in the space and scale of relevance to geography; that is, at or near the surface of E ...
containing locations that are within a specified distance of that feature, the buffer zone (or just buffer).
A buffer is likely the most commonly used tool within the
proximity analysis methods.
[Wade, T. and Smmer, S. eds. ]
A to Z GIS
'
History
The buffer operation has been a core part of GIS functionality since the original integrated GIS software packages of the late 1970s and early 1980s, such as
ARC/INFO
ArcInfo (formerly ARC/INFO) is a full-featured geographic information system produced by Esri, and is the highest level of licensing (and therefore functionality) in the ArcGIS Desktop product line. It was originally a command-line based system. T ...
,
Odyssey
The ''Odyssey'' (; grc, Ὀδύσσεια, Odýsseia, ) is one of two major Ancient Greek literature, ancient Greek Epic poetry, epic poems attributed to Homer. It is one of the oldest extant works of literature still widely read by moder ...
, and
MOSS
Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...
. Although it has been one of the most widely used GIS operations in subsequent years, in a wide variety of applications, there has been little published research on the tool itself, except for the occasional development of a more efficient algorithm.
Basic algorithm
![GIS Buffer](https://upload.wikimedia.org/wikipedia/commons/8/8a/GIS_Buffer.png)
The fundamental method to create a buffer around a geographic feature stored in a
vector data model, with a given radius ''r'' is as follows:
* Single point: Create a circle around the point with radius ''r''.
*Polyline, which consists of an ordered list of points (vertices) connected by straight lines. This is also used for the boundary of a polygon.
# Create a circle buffer around each vertex
# Create a rectangle along each line segment by creating a duplicate line segment offset the distance ''r'' perpendicular to each side.
# Merge or dissolve the rectangles and circles into a single polygon.
Software implementations of the buffer operation typically use alterations of this strategy to process more efficiently and accurately.
Planar vs. geodesic distance
Traditional implementations assumed the buffer was being created on a planar
cartesian coordinate space (i.e., created by a
map projection
In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and longitud ...
) using
Euclidean geometry
Euclidean geometry is a mathematical system attributed to ancient Greek mathematics, Greek mathematician Euclid, which he described in his textbook on geometry: the ''Euclid's Elements, Elements''. Euclid's approach consists in assuming a small ...
, because the mathematics and computation involved is relatively simple, which was important given the computing power available in the late 1970s. Due to the inherent distortions caused by map projections, the buffer computed this way will not be identical to one drawn on the surface of the Earth; at a local scale, the difference is negligible, but at larger scales, the error can be significant.
Some current software, such as Esri
ArcGIS Pro
ArcGIS Pro is desktop GIS software developed by Esri, which replaces their ArcMap
ArcMap is the main component of Esri's ArcGIS suite of geospatial processing programs, and is used primarily to view, edit, create, and analyze geospatial data. ...
, offer the option to compute buffers using ''geodesic distance'', using a similar algorithm but calculated using
spherical trigonometry
Spherical trigonometry is the branch of spherical geometry that deals with the metrical relationships between the sides and angles of spherical triangles, traditionally expressed using trigonometric functions. On the sphere, geodesics are gr ...
, including representing the lines between vertices as
great circle
In mathematics, a great circle or orthodrome is the circular intersection of a sphere and a plane passing through the sphere's center point.
Any arc of a great circle is a geodesic of the sphere, so that great circles in spherical geomet ...
s.
Other implementations use a workaround by first reprojecting the feature to a projection that minimizes distortion in that location, then computing the planar buffer.
Options
GIS software may offer variations on the basic algorithm, which may be useful in different applications:
* Endcaps at the end of linear buffers are rounded by default, but may be squared off or a butt end (truncated at the final vertex).
* Side preference may be important, such as needing the buffer on only one side of a line, or on a polygon, selecting only the outer buffer or the inner buffer (sometimes called a ''setback'').
* Variable width, in which the features in a layer may be buffered using different radii, usually given by an attribute.
* Common buffers, in which the buffers for each feature in a layer are dissolved into a single polygon. This is most commonly used when one is not concerned about which feature is near each point in space, only that a point is nearby some (anonymous) feature.
See also
*
Dilation (morphology) Dilation (usually represented by ⊕) is one of the basic operations in mathematical morphology. Originally developed for binary images, it has been expanded first to grayscale images, and then to complete lattices. The dilation operation usually u ...
(positive buffer)
*
Erosion (morphology)
Erosion (usually represented by ⊖) is one of two fundamental operations (the other being dilation) in morphological image processing from which all other morphological operations are based. It was originally defined for binary images, later bei ...
(negative buffer)
External links
OGC ST_Buffer function(
PostGIS
PostGIS ( ) is an open source software program that adds support for geographic objects to the PostgreSQL object-relational database. PostGIS follows the Simple Features for SQL specification from the Open Geospatial Consortium (OGC).
Technica ...
implementation)
buffer functionin turfjs
in JTS, the library at the foundation of many open-source GIS implementations
command in GRASS
tool in Esri ArcGIS Pro
References
Geographic information systems
Geometry
Spatial analysis
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