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I have estimated and reclassify my kernel densities and I would to calculate the area of each value. How could I do it?

My Projected Coordinate System is WGS84 World Mercator. My pixel size is 10000 x 10000. Linear unit: Meter (1).

Mapperz
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Sofia Margaroni
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2 Answers2

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A kernel function represents a Gaussian distribution of weighted or unweighted density base on characteristics of the specified kernel (eg., sigma, distance, alternative distributions) so, area is a fairly vague term. Commonly the "area" of a KDE is articulated as the percent volume or isopleth contour, at least in the wildlife resource selection literature. Once a given volume is output, the area is just the total cell area of the percent volume. There is a function, "raster.vol", in the spatialEco R package or if using ArcGIS in the Home Range Tools that will output percent volumes.

Jeffrey Evans
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As far as I can understand from your question, this is a technical issue. As such this answer will point to some tools/processes that may help you to calculate the area of each class. Nevertheless, you should use an equal-area coordinate system to get correct results. Thus, at start the data must be re-projected.

I suggest two approaches to calculate the area for each class: a raster and a vector approach. I personally prefer the raster approach. Yet it also depend on other data types involved in post processing.

  • Raster approach uses the Build Raster Attribute Table tool. It create a frequency table, to wit it counts how many times each cell value appears. Your 10 by 10 KM resolution means that each cell has an area equals to 100 squared KM. Thus a simple multiplication of the frequencies by the cell's area will result in the total area of each class. Note that using this tool requires the input raster to be of type short or long integer.
  • Vector approach involves a conversion to polygon. Note that by default the output vectors are simplified, an will sum up to a different area. It can be easily be controlled from the tool's options. A second tool will include the use of calculate geometry to get the area of each feature.
dof1985
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  • It is crucial that these calculations be carried out using an equal-area coordinate system. – whuber Jun 30 '16 at 19:55
  • @whuber I agree, however I don't believe that this was the focus of the question. I did however point out the relevancy and importance of the coordinates system being used – dof1985 Jun 30 '16 at 20:01
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    Please don't rely on referring to comments--they can disappear at any time. If that comment were not there, your answer would likely mislead readers. Even with that comment, newbies to GIS could easily overlook the fact that it's crucial to reproject the raster into an equal-area projection. This issue isn't merely relevant, it's essential for getting correct results. – whuber Jun 30 '16 at 20:04