[R-sig-Geo] how to calculate centroid (or centre of gravity) of a population (count data)

[Marcelino de la Cruz]

Hi Diego,

it seems to me that what you want to compute are weighted centroids.

Here some advice is given (it is for polygons but you can get the idea):

https://stat.ethz.ch/pipermail/r-sig-geo/2016-February/024107.html

Cheers,

Marcelino



El 20/04/2016 a las 8:45, Diego Pavon escribió:
> Dear all
>
> I am working with count data and I want to assess whether the centre of
> gravity of the population (centroid or mean latitude?) has change over
> time, indicating some redistribution or shift ongoing. To simplify, let's
> say that I have ca. 2000 sites censused in two consecutive years (same
> sites censused both years - all sites) and the abundance (count) of the
> species registered.
>
> I first thought about doing a kernelUD (package adehabitatHR) but
> apparently this only takes into account the location of the sites to
> calculate the kernel and then the centroids. Thus, since I have the exact
> same sites in both years, the centroids for year 1 and year 2 are the same.
> In my case, what I would like to do is to calculate that centroid but
> taking into account the counts, because a site that had 3 individuals in
> both years can't have the same weight than a site that hosted 3000
> individuals when calculating the centroids.
>
> So, what I would like to have is the centroid (or centre of gravity) of the
> counts not of the sites surveyed (which is what adehabitatHR does,a s far
> as I understood).
>
> Do you have any suggestions which package other than adehabitatXX to use
> for this purpose? Or if this can be done with adehabitat?
>
> Thank you very much for your help.
>
> Diego
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