ROADDENSITY

 

creates a polygon coverage (and two grids) of focal line density from a line coverage.  Density is calculated using a circular moving window.  The value of each cell is the density of lines within the circular window centered on the cell.  The default window size is 1 square mile.

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ROADDENSITY <road_cover> <clip_cover> {output} {cellsize} {windowsize} {remap_table}

 

ARGUMENTS

 

<road_cover> - the existing coverage containing arcs from which line density will be calculated.

 

It must contain arcs (AAT).

 

It must also have map units of FEET or METERS which have been defined in the map projection (e.g. using ARC PROJECTDEFINE.)

 

When run from ARC, all arcs in the <road_cover> will be used to calculate density.  However, when run from GRID, if a subset of arcs have be RESELECTed, then only these arcs will be used in the analysis.

 

Note: If you want to include roads outside the {clip_cover} in the road density analysis, (a good idea to minimize edge effect) make sure the roads extend beyond the clip coverage by at least the radius of the window (e.g. 908 meters is the radius of a 1 square mile circle, but it should be padded a little to account for the {cellsize}).  And there is no problem if they extend far beyond that.

 

<clip_cover> - an existing polygon coverage used to clip out the results.

 

The {output} grids and coverage will be clipped to the exterior boundary of the polygons in this clip coverage.

 

Additionally the {output} grids and coverage will be clipped to the SETWINDOW, if it has been set to coordinates.

 

{output} - the name for the output grid of line density.  And the base name of the {output}_GP grid of density groups and the {output}_P coverage of density polygons.  The default {output} name is DENSITY.

 

In other words, ROADDENSITY creates 3 maps:

 

{output} is a floating-point grid of line density.  The value of each cell is the density of lines within a circular window centered on the cell.  Density is expressed in miles per square mile.  The size of the circular window is specified by {windowsize}.

 

{output}_GP is an integer grid of density RECLASSified into groups using the {remap_table}.  When no {remap_table} is specified, then default ranges are used.  See {remap_table}.

 

{output}_P is a polygon coverage of density created by vectorizing the {output}_GP grid.

 

The {output}_P PAT contains 3 user items: DENSITY_CODE, DENSITY, and ACRES.  DENSITY_CODE is the ID number assigned to the density group.  DENSITY is the description of the group, e.g. >0.5-1 mi/mi2.  And ACRES is just that.

 

The output maps may not be named the same as any existing file or directory.

 

{cellsize} - the processing cell size.

 

The default is the current setting of SETCELL.  If SETCELL isn't set, then cell area defaults to 1 acre (i.e. a cell size of 63.61.. meters or 208.71.. feet).

 

WARNING - Processing time is greatly affected by cell size.  Halving the cell size can result in 2 ^ 4, or 16 times the processing time, and may not greatly improve the results.

 

{windowsize} - the size of the moving window within which density is summarized for each cell in the {output} grid.

 

The units of {windowsize} are square miles.  The default value is 1.

 

{remap_table} - a remap table used to RECLASSify the density values into broader groups in the {output}_GP grid and {output}_P coverage.

 

This must be an ASCII remap table.  The GRID RECLASS function is used to perform the reclassification.  See RECLASS for more information on ASCII remap tables.

 

By default a temporary remap table is created as follows:

 

0 0 : 0

0 0.5 : 1

0.5 1 : 2

1 1.5 : 3

1.5 2 : 4

2 2.5 : 5

2.5 3 : 6

3 999 : 7

 

 

NOTES

 

- ROADDENSITY runs from the ARC and GRID modules of ARC/INFO.

 

- When using ARC/INFO 7.0.4 (or 8.3 on AIX) the actual size of the moving window will likely not exactly equal the specified size, since the window is built from whole cells.  For example, when {cellsize} is 30 meters and a {windowsize} of 1 is specified, the actual window will contain 2,821 cells, ca. 0.98 square miles.  However, this is taken into account when calculating density.

 

-     When using ARC/INFO 7.1+ the GRID LINEDENSITY function is used to calculate density, the specifics of which are not stated in ArcDoc.

 

- For more options re. the calculation of line density, see the FOCALDENSITY tool.

 

- ROADDENSITY can be run from the command line or from a menu.  When the global variable: .R6MODE is set to MENU, then running ROADDENSITY will popup a menu, unless all the required arguments are provided.

 

 

DISCUSSION

 

USE - ROADDENSITY will work with any line data, but it was written to help aid and standardize the calculation of road density.  For more information refer to the "Standardization of Road Definitions and GIS Procedures for Calculating Road Definitions", March 13, 1997, File Code: 2670, Route To: 7700.