|
|
| GIS Cookbook: Background - Background Information about Buffers |
Keywords: Buffer, points, lines, polygons, raster, vector, topography
Category: Buffers
Software: ArcView 3.2
Background: When buffering, the user creates a new object that displays and identifies which areas are found within a specified distance of the original object. The buffer operation results in new boundaries around points, lines, or polygons.
*Examples of buffers are listed in the description section of the recipe*
A common concern among people using buffers is figuring out what buffer width to use in their map or analysis. Because buffer width designation can vary substantially between projects, various factors could be used. These factors include:
1) Input from the Source: An attribute of the object being buffered is used to determine buffer width. For example, buffer width could depend on the amount of chemical spilled from a refinery
2) Internal Factors Within a Buffer: Variables affecting the area inside the buffer boundaries such as topography within the buffer and weather conditions. eg. If the object being buffered lies where annual winds blow out of the east, the buffer distance around the object will probably be greater to the west of the object
3) Outcomes: What is probably going to happen because of variables inside and or outside the buffered area. An example would be if certain populated areas are given priority evacuation due to the chemical spill
Pros: There are many advantages to using buffers in GIS. First of all, buffers can be applied to both vector and raster data, which is abnormal for most GIS operations. A buffer made in raster format is unlike one made in vector. In vector a new object is formed in the shape of a buffer, however in raster, cells are merely classified to whether they are inside or outside the buffer zone. A good example of a raster application is shown below with travel times.
Another advantage to using buffers in GIS is the ability to use multiple rings for varying buffer distances. Because of this, if you want to show that certain distances have more impact than others you do not need to create several buffers. Finally, two other advantages specific to ArcMap include the ability to buffer coverages, and the choice of whether to round area, or line buffer edges. These advantages add precision to your results.
Cons: There are few disadvantages for using buffers in Arc View and Arc Info. One disadvantage however, is of topography. When buffering at a certain distance you are measuring that distance as the crow flies and you are not taking in account the differing slope of the land. For example if regions to the east of the point, line or area being buffered have a high slope and regions to the west have minimal elevation increase, your buffered regions will cover different total areas on each side. But when you specify a buffer distance such as ten miles, ten miles will not take in account slope, and thus may skew results.
|
| Authored by: Ethan Sundilson Modified: 9/12/02 |
|
Copyright © 2002-2015 by Regents of University of California, Santa Barbara
Cookbook: Ben Sprague, Ethan Sundilson, Carlin Wong, Sam Ying
|
|
|