Buffer

• As described in How Buffer works, an important feature of the Buffer tool is the Method parameter, which determines how buffers are constructed. The two basic methods for constructing buffers, Euclidean and geodesic, are described as follows:

  • Euclidean buffers measure distance in a two-dimensional Cartesian plane, where straight-line or Euclidean distances are calculated between two points on a flat surface (the Cartesian plane). Euclidean buffers are the more common type of buffer and are appropriate when you're analyzing distances around features in a projected coordinate system that are concentrated in a relatively small area (such as one UTM zone).
  • Geodesic buffers account for the actual shape of the earth (an ellipsoid, or more properly, a geoid). Distances are calculated between two points on a curved surface (the geoid) as opposed to two points on a flat surface (the Cartesian plane). You should always consider creating geodesic in the following circumstances:
    • Your input features are dispersed (cover multiple UTM zones, large regions, or even the entire globe).
    • The spatial reference (map projection) of your input features distorts distances to preserve other properties such as area.
    Geodesic buffers may appear unusual on a flat map. When displayed on a globe, however, these buffers will look correct (you can also use the ArcGlobe or ArcGIS Earth applications to view geographic data on a three-dimensional globe). For more information, see How Buffer works.

  The Method parameter determines how buffers are created.

  • Planar (method="PLANAR" in Python) is the default option. This option will automatically determine which method to use based on the coordinate system of the input.
    • If the input features have a projected coordinate system, Euclidean buffers will be created.
    • If the input features have a geographic coordinate system and you specify a Buffer Distance in linear units (meters, feet, and so forth, as opposed to angular units such as degrees), geodesic buffers will be created.
    • This option produces the same result as the Buffer tool prior to ArcGIS 10.3.
  • Geodesic (method="GEODESIC" in Python) creates a shape-preserving geodesic buffer regardless of the input coordinate system. The shape-preserving geodesic buffer densifies the input features prior to creating the output geodesic buffers to create buffers that more closely represent the input features' shape. If you are concerned about the shape of your buffers and how closely their shape matches the original input features, it is recommended that you investigate using this option, particularly when your input data is in a geographic coordinate system. In some cases, this may take more time than the geodesic buffer created using the Planar option, but the result is a buffer that more accurately matches the shape of the input feature.

  You can change the coordinate system of a feature class using the Project tool, or you can set the Output Coordinate System geoprocessing environment before executing the Buffer tool, and this coordinate system will be used when creating buffers.

  When using the Planar method, you can improve the accuracy of buffers created with projected inputs using a projection that minimizes distance distortion, such as an Equidistant Conic or an Azimuthal Equidistant projection, and is geographically appropriate for your input.

• When buffering features in a projected coordinate system with output to a geodatabase feature class, the geometries created may contain circular arc segments (when buffering points, the output will always be circular arcs). If buffers containing circular arcs are reprojected to a different coordinate system, the location and size of the original buffers will be transformed, but the shape of the buffers will not change, causing the reprojected buffers to no longer accurately represent the area covered by the original buffer. If you reproject buffers containing circular arcs, first use the Densify tool to convert circular arc segments to straight lines, and then reproject the densified buffers.

• The output feature class will have a BUFF_DIST field that contains the buffer distance used to buffer each feature in the linear unit of the input's coordinate system. When using the Geodesic method to create buffers, the buffer distance entered will be converted to meters in all cases.

  If a field named BUFF_DIST exists in the input, its values will be overwritten in the output. If a Dissolve Type of All or List (ALL or LIST in Python) is used, the output will not have this field.

• The output feature class will have a ORIG_FID field that contains the feature ID of the input feature for which the buffer was created. If a field named ORIG_FID exists in the input, its values will be overwritten in the output. If a Dissolve Type of All or List is used, the output will not have this field.

• When buffering polygon features, negative buffer distances can be used to create buffers inside the polygon features. Using a negative buffer distance will reduce the polygons' boundaries by the distance specified.

  If the negative buffer distance is large enough to collapse the polygon to nothing, a null geometry will be generated. A warning message will appear, and no null geometry features will be written to the output feature class.

• If a field from the input is used to obtain buffer distances, the field's values can be either a number (5, for example) or a number with a valid linear unit (5 Kilometers, for example). If a field value is a number, it is assumed that the distance is in the linear unit of the input's spatial reference (unless the input is in a geographic coordinate system, in which case, the value is assumed to be in meters). If the linear unit specified in the field values is invalid or not recognized, the linear unit of the input's spatial reference will be used by default.

• The Dissolve Field(s) parameter Add Field button is used only in ModelBuilder. In ModelBuilder, where the preceding tool has not been run or its derived data does not exist, the Dissolve Field(s) parameter may not be populated with field names. The Add Field button allows expected fields to be added to the Dissolve Field(s) list to complete the Buffer tool dialog box.

• Side Type (line_side) options Left, Right, and Outside only (LEFT, RIGHT, and OUTSIDE_ONLY in Python) and the End Type (line_end_type) option Flat (FLAT in Python) are only available with an Desktop Advanced license.

The following Python window script demonstrates how to use the Buffer tool.

Find areas of suitable vegetation that exclude areas heavily impacted by major roads.

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