Hawth's Analysis Tools for ArcGIS

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 Summary

POINT REDISTRIBUTION TOOL
Input: a point layer representing the location from which points are redistributed, a polygon layer representing the boundary of the area inside which the points can be redistributed, and a raster layer representing a probability density surface
Output: a point layer of redistributed points and optionally raster layers depticting the functional distance from the source points
Features:

  • The function of this tool is to redistribute N points from each source location to new locations inside a polygon boundary that are selected using a probability density surface in the form of a raster layer. The souce point layer must contain three attribute fields: i) a unique ID field (preferably a long integer), ii) an integer field representing the number of points to redistribute, and iii) an integer or double field representing the radius over which points can be redistributed. Note that this calculation uses functional distance, not straight line distance.

Limitations:

  • for certain irregularly shaped polygons this program will run more slowly
  • all the input data must be in the same projected coordinate system


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 Example

Figures A-D. In this example, an irregularly shaped lake (A) has three docks (pink points in Fig A). The probability of use of different portions of the lake is shown in B (red is low probability, blue is high probability). The attribute table of the dock point layer contains fields that represent the number of points to redistribute (i.e. in this example 100 boats are redistributed from each dock) and the maximum distance from the source point these redistributed points can be located (10km in this case). Note that it is not straight line distance, but functional distance that is used to determine this boundary (Fig C shows the 10km functional distance raster for one of the docks; the 10km distance is green in this colour scheme). The probability surface is used to distribute the boats on the lake (zoomed in example shown in Fig D). an irregularly shaped raster layer is used as the reference layer (A). (Note that NoData cells have been coloured grey in order to display the true extent of the raster layer). 1000 random points (red dots) were generated and the option to prevent them from occurring in NoData cells was activated.

Figures C & D. Here a polygon layer is being used as the reference layer (C) and exactly 5 random points (red dots) per polygon are being generated (D).

 Help

Getting started. Three layers must be loaded into ArcMap before starting this tool. The first is a point shapefile representing the source locations with the following attribute fields: i) a unique ID field (preferably long integer), ii) a field representing the number of points that are redistributed from that source (integer), and iii) a field representing the functional distance radius to use from that source (a double precision number or integer). The second layer is a polygon layer representing the boundary inside which the points can be redistributed. The third layer is the raster layer representing the probability surface.

Setting the output folder. When you press the yellow folder button an interface opens that allows you to select an output folder. The output folder should be completely empty. You can either pre-create the folder in Windows Explorer, or use the "Create New Folder" button in the interface. Note that when you navigate to the folder that contains your output folder (i.e. the parent folder) you need to single-click on the output folder and then press the Add button - if you double-click the output folder, it will simply open that folder and wait for you to select a folder (not what you want to do). Thus this interface for selecting folders can be a little confusing (just remember to single-click, not double-click).

Saving the functional distance rasters as output. If you select the option to save the functional distance rasters as output, then one raster will be created for each source point and placed in a subfolder called "fdr" (functional distance raster) in the output folder.

The redistributed point output. The output of this tool is a point shapefile containing the redistributed points from all the source points. The attribute table of this layer contains the unique ID value of the source point (so you can distringuish which points can from which sources), and the number of point (i.e. if you specified 100 points to redistribute, the points will be numbered 1-100).

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