[R-sig-Geo] Extract() fails to return data for boundary admin units

[Bacou, Melanie]

Chris,
Thanks, using `weights=TRUE` to compute the means fixed the problem.
Perfect, --Mel.


On 10/18/2016 11:10 AM, chris english wrote:
>
> Mel,
>
> Looking at detail in cjg.png the northmost missing data island shows 
> approx 20-25 in Southern three quarters and 0-5 the small North at tip 
> of island. Directly above this 0-5 another coastal 0-5.
> If a substantial east-west scarp bisected the island it might explain. 
> I would otherwise expect a very slight mismatch in projection, a thing 
> I often have problems with.
>
> Though reading raster::extract it looks like you want to employ the 
> weights are if your polys are relatively smaller than your cells.
>
> HTH
> Chris
>
>
> On Oct 18, 2016 4:35 PM, "Bacou, Melanie" <mel at mbacou.com 
> <mailto:mel at mbacou.com>> wrote:
>
>     Hi,
>     I'm summarizing biophysical rasters (UDEL precipitation and
>     temperature) across administrative units for countries in Africa
>     using (pseudo code):
>
>     raster::extract(udel, admin, fun=mean, na.rm=T, small=T)
>
>     Out of the 756 units I need data for, extract() fails to return
>     means for a few coastal units (in red on the maps below) even
>     though the rasters show data at these locations.
>
>     Is there a particular reason why this might happen? Shall I look
>     for possible geometry errors in my source shapefiles, or could
>     there be another reason?
>
>     Maps here:
>     https://dl.dropboxusercontent.com/u/30925475/eclgcdmhapfplaml.png
>     <https://dl.dropboxusercontent.com/u/30925475/eclgcdmhapfplaml.png>
>     https://dl.dropboxusercontent.com/u/30925475/lmkgmdoohpmhdcjg.png
>     <https://dl.dropboxusercontent.com/u/30925475/lmkgmdoohpmhdcjg.png>
>
>     Thanks for any tip. --Mel.
>
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