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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