A spatial analysis question:

I'm trying to compare species distributions and specifically overlap between two species (Water Vole and European Rabbit) that are competitive species. I also want to look how the common shared predator the Minx causes this distribution.

Can anyone suggest what ArcTools I can use?

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    You would likely be interested in the "UDOI" calculation and in the methods used to carry it out. The actual calculations depend heavily on what kind of data you have. For instance, do you have points of observation? Or perhaps has someone already delineated distribution ranges for you (as polygons)? – whuber Jan 13 '14 at 18:03
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    you might want to indicate what format your data is in(raster/vector) and the type/detail of the data (point observations vs. extent polygon) – TDavis Jan 13 '14 at 18:03
  • My data is points of observation (x,y coordinates) of each species. These are presently in vector data. – Becky Jan 15 '14 at 15:11
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    buffer each point and then intersect the buffers would give you an overlap of Territory. You mention arcgis and spatial analyst, if vector data then the standard geoprocessing tools will be the best route resources.arcgis.com/en/help/main/10.2/index.html#//… – Mapperz Jan 15 '14 at 15:19
  • If I do this, can I get a numerical output of the overlap? Ie. Actual numbers I can discuss? – Becky Jan 15 '14 at 15:29

Using Spatial Analyst in ArcGIS for this the Weighted Overlay (Spatial Analyst) would be a good way to find the coverage you are looking for:

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All input rasters must be integer. A floating-point raster must first be converted to an integer raster before it can be used in Weighted Overlay. The Reclassification tools provide an effective way to do the conversion.

Each value class in an input raster is assigned a new value based on an evaluation scale. These new values are reclassifications of the original input raster values. A restricted value is used for areas you want to exclude from the analysis.

Each input raster is weighted according to its importance or its percent influence. The weight is a relative percentage, and the sum of the percent influence weights must equal 100.

Changing the evaluation scales or the percentage influences can change the results of the weighted overlay analysis.


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  • In comparing species distributions why would you want to weight the overlay and how would one derive relevant weights? This does not make sense from a process standpoint. – Jeffrey Evans Jan 13 '14 at 18:40
  • What would you suggest instead? I want to look at the overlap between species, but need a numerical output to analyse rather than just visual. – Becky Jan 15 '14 at 15:06

In the vector format, the area of overlap between two areas is the intersection. (intersect (analysis) tool in the toolbox. You can thus compute the intersection between the "minx range" and each other range, then you compute the area of the intersection in a new field using "calculate geometry" (not necessary with geodatabase). If you have several polygon, right-click on the area field and ask the statistics.

But if you talk about spatial analyst, I assume that you work with raster. Then you have a continuous field and the overlap is defined by the minimum of the two rasters. You can do this with cell statistics.

Another way to visualize your distributions is simply to use a difference between the two rasters. If you do A-B, negative value indicate that you have more B than A. You can do it with the raster calculator (map algebra).

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  • My data is in vector format, I did not know there was a similar tool available. Thank you. I need to be able to analyse whether there is more of an overlap between voles and minx, or rabbit and minx. – Becky Jan 15 '14 at 15:04

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