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I have a raster file on precipitation and I want to create zonal statistics as a table using a shape file wiht boundaries of countries across the world. However it appears that I need to take into account that in different latituted the corresponding area is different and thus I need to weight my statistic (mean etc) for area. Any suggestions on how I can do that?


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I should clarify that I work with ARCGIS 10.1 – An_Li Mar 18 '13 at 12:43
If I understand your problem correctly: use an equal-area projection. Then you do not have to "weight you statistic". – Jens Mar 18 '13 at 15:23
An_Li, @Jens offers the best solution: use an equal-area projection. However, if you wish to avoid reprojecting (and the resampling that necessarily goes along with that), your idea is quite workable. At the very end of…, I describe how to obtain a weighted (zonal) average. For weights, use the cosine of the latitude. – whuber Mar 18 '13 at 18:04

If you are open for other GIS tools then have a look at SAGA-GIS:

There is a module called "Grid Statistics for Polygons" which does exactly what you are looking for.

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Thanks for the comments. I will try the equal area projection. Unfortunately I am new to ARC GIS so I already have difficulties with already, let alone moving to a different software. – An_Li Mar 18 '13 at 15:51

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