Buffer (Coverage) (ArcInfo only)

Usage tips

• Small sliver polygons may be created by BUFFER. They can cause problems when coded as nonbuffer areas inside buffer zones. Remove them with Eliminate.

• Features will not be buffered if their buffer distance is zero. If you do not want to buffer a feature in the input coverage, give it a buffer distance value of zero in a buffer item or of DIST in a buffer table.

• Negative and positive distances can be used for buffer distance with the POLY option. It is possible to shrink some polygons and grow others in the same coverage when the buffer item contains positive and negative numbers.

• When performing a BUFFER on a coverage that contains island polygons, all the polygons with a buffer distance greater than zero get buffered. However, since the island buffer is entirely within its surrounding polygon buffer, it is dissolved into the surrounding polygon during Buffer's dissolve phase and the island buffers will not be visible.

• Nodes can be buffered on coverages with or without an NAT. If there is no NAT, the nodes in the AAT must be numbered (FNODE# and TNODE# must be greater than zero). Run Renumber Nodes if the node numbers are zero.

• The ROUND, FLAT, FULL, LEFT, and RIGHT options apply only to line data.

• The LEFT and RIGHT options generate buffers at the left or right of a line. Caution must be exercised in interpreting the "left" or "right" of a line. A single line segment defines two half planes, cutting a rectangular buffer into two clearly defined left and right sections. When connecting line segments, points that are on the left side of one segment may be on the right side of another connecting segment. This ambiguity can be prevented by a concept of "not crossing over the line".

• The LEFT and RIGHT options use the topological left and right of the line, so line topology must be present for the use of these options. To access the Line buffer styles, use Build on the input coverage with LINE and NODE.

• The BUFFER function works in Euclidean space and uses a two-dimensional algorithm. A buffer will be the same width no matter what the coordinate system is. It will not reflect the curvature or the shape of the earth. For the best results, generate the buffer in a map projection that minimizes distortion in the area of interest.

• For buffers around lines, the fuzzy tolerance for the output coverage may not be the same as the fuzzy tolerance of the input coverage. The output tolerance may be reset as a function of the buffer distance. This may happen for larger buffer distances and reflects the progressively courser approximation of a circle with a fixed number of straight line segments. If this effect is to be avoided, a buffer can be "grown" in a number of steps. First, run BUFFER with the LINE option using a small buffer distance, then run a number of buffers on this using the POLY option until you achieve the desired resultant buffer distance. Fuzzy tolerance changes only for buffers around lines; it does not change for buffers around polygons.

• The coordinate precision of the output coverage is determined by the current processing rule as set by the Precision for Derived Coverages environment setting. If the processing rule has not been established during the current session, then the processing rule will be HIGHEST. This means that BUFFER will create an output coverage in the same precision as the input coverage.

• On both single-precision and double-precision coverages, BUFFER calculates a minimum tolerance based on the mathematical precision of the coverage (based on the width of the BND and the number of decimal places). If the calculated minimum tolerance is greater than the entered fuzzy tolerance, the calculated minimum tolerance is used.

• The projection file (PRJ) will be copied to the output coverage.

• Learn more about using caution with the Left and Right options of Line buffer style.

• Learn more about how the default fuzzy tolerance is calculated.

• The following environments affect this tool: derivedPrecision, newPrecision, projectCompare, scratchWorkspace, and workspace.

Command line syntax
An overview of the Command Line window
Buffer_arc <in_cover> <out_cover> {LINE | POLY | POINT | NODE} {buffer_item} {buffer_table} {buffer_distance} {fuzzy_tolerance} {ROUND | FLAT} {FULL | LEFT | RIGHT}

Command line example

Buffer_arc c:\base_data\road c:\base_data\roadbuf LINE # # 200 0.5 ROUND FULL

Scripting syntax
About getting started with writing geoprocessing scripts
Buffer_arc (in_cover, out_cover, feature_type, buffer_item, buffer_table, buffer_distance, fuzzy_tolerance, buffer_shape, buffer_side)

Script example

import arcgisscripting
gp = arcgisscripting.create()

gp.workspace = "c:/base_data"
gp.toolbox = "arc"
gp.buffer_arc("road", "roadbuf", "line", "#", "#", "200", "0.5",  "round", "full")