AREAOFINF

Description

AREOFINF converts a point layer to a raster layer representative of the influence or attractiveness of each point in the layer.

Parameters

Name	Type	Length	Value range
InputPoints: Point Layer: Input point layer *	Vector port	1 - 1
Bitmap: Bitmap Mask: Input bitmap segment or layer	Bitmap port	0 - 1
InputArea: Bounding Area: Georeference layer	GEO port	0 - 1
Output Raster: Output raster channel or layer	Raster port	0 - 1
Attribute Weight	String	0 - 1	ATTRIBUTE, Z-COORD, others Default: Z-COORD
Exponent	Float	0 - 1	0 - Default: 2
Source Attributes	String	0 - 1	COPY, JOIN Default: COPY
Pixel X Size	Real	0 - 1	0.0 -
Pixel Y Size	Real	0 - 1	0.0 -
Report	String	0 - 192	See parameter description

* Required parameter

Parameter descriptions

InputPoints: Point Layer: Input point layer

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

Bitmap: Bitmap Mask: Input bitmap segment or layer

Specifies the bitmap segment to sample data from the input vector point data.

A bitmap layer restricts the region when generating the weighted average. The results are generated 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.

InputArea: Bounding Area: Georeference layer

Specifies the georeferencing of the resulting raster layer.

The specified bounding area 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.

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.

The raster type is either 8U, 16U, or 32R, depending on the number of points used.

Attribute Weight

The input point data layer should contain a column that assigns a value to each point as an indication of its "attractiveness" or its intended contribution to the final output. This is referred to as a weight; the higher the weight value, the greater the influence exerted. If no attributes exist, the "z" value of the points is used for the weight.

Exponent

Controls the effect of the distance decay. The higher the value, the greater the effect of the distance decay. The default value is 1.

Source Attributes

Specifies whether the attributes are copied or joined. If an invalid value is specified, this parameter defaults to COPY.

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, AREAOFINF defines a catchment area around each point. A catchment area is an area surrounding a point in which any location is more attracted to that point than to any other point. This results in a one-to-one relationship: one area to one point. The higher the density of points, the smaller the catchment area. Conversely, data with a low density of points creates large catchment areas.

This function differs from THSNPOLY in that it uses a weight and distance-decay factor to define the catchment areas.

One pixel value is assigned to each point.

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).