AREAPROB

Description

Parameters

Parameter descriptions

InputPoints: Point Layer: Input point layer

Contains the input point layer. If the projection of the point layer is different than the projection of the output raster, each point will be reprojected to the raster projection before the calculation is performed.

InputArea: Bounding Area: Georeference segment or layer

Specifies the georeference segments that apply to the projection.

DBGEO contains the geoereferencing of the resulting raster layer and specifies the projection, geographic extents, and size (pixels/lines) of the resulting raster layer. The georeferencing can also be set from the bitmap input layer if it is specified. If this parameter and the bitmap layer are not used, the projection of the raster layer will be the same as that of the point layer. The geographic extents of the raster layer are determined by the extents of point layer and the pixel size parameters.

Bitmap: Bitmap Mask: Input bitmap segment or layer

Specifies the bitmap segment to sample data from the input image data.

A bitmap layer restricts the region when generating the weighted average. The results are gerenated inside the bitmap layer (value 1), and pixels falling outside the bitmap (value 0) are given a "No Data" value. The bitmap layer, if used, also defines the georeferencing of the output raster.

Output: Output Raster: Output raster channel or layer

Specifies the output raster channel that receives the raster layer derived from the point layer.

The georeferencing will either be determined from the georeferencing information, the bitmap layer, or calculated using the point layer extents and the pixel X/Y size.

Source (Focus only)

Indicates whether to use the currently selected point or to enter the Shape ID for the point. The attractiveness for this point is calculated. This parameter is only available through the Focus Algorithm Librarian.

ShapeID

Specifies the Shape ID of the point used in the calculation.

Attribute Weight

Exponent

Controls the effect of the distance decay. The higher the value, the greater the effect of the distance decay. If this parameter is not specified, this parameter is set to 2.0.

Pixel X Size

Specifies the x-pixel size for the output raster layer. This parameter is not required and is disabled if the georeferencing is specified by the InputArea port.

Pixel Y Size

Specifies the y-pixel size for the resulting raster layer. This parameter is not required and is disabled if the georeferencing is specified by the InputArea port.

Report

Specifies where to direct the generated report.

Available options are:

• LOG: generates a report on the terminal (default)
• <modulename.RPT>: appends a report to the module's RPT file
• DISK: generates a report on file "IMPRPT.LST"

Details

The attractiveness of a point in a gravity model is inversely proportional to distance and is directly related to the perceived attractiveness of the point itself. The point data must include weight values representing the attractiveness of each point. A weight is a numeric value assigned to each point as an indication of its importance or its intended contribution to the final output. You must also specify a distance-decay factor that calculates the diminishing attractiveness with the increasing distance. The greater the distance to the point, the less attractive the point becomes.

Using this information, AREAPROB generates areas that indicate the probability of any location within that area being attracted to the specified point. The output values are expressed as a percentage, with 0 indicating no attractiveness and 100 indicating maximum attractiveness.

The probability function is based on Reilly's improvements on the Huff model.

References

Ken Jones and Jim Simmons, Location, Location, Location: Analyzing the Retail Environment (Methuen, Toronto, 1987), pp 114-116, 263-269.

Avijit Ghosh and Sara L. McLafferty, Location Strategies for Retail and Service Firms (Lexington Books, Toronto, 1987)