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I have precipitation data that I would like to average over each municipal unit in a boundary layer. First, how do I average the rainfall spatially by each administrative unit?

Second, the rainfall values are not unique to each administrative unit, and so I am not sure how to join them to the attributes table of the admin boundary layer. Although they will be unique once they are averaged, in the sense that there is one averaged value per administrative unit. If this is true, which variable do I merge on? Do I need to create something new?

I am using the end result (an average rainfall value for each municipal unit) in STATA, hence the need to export the attribute table. The program I'm using is ArcMap.

I did something like this years ago but cannot remember...any help would be greatly appreciated!

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What form are these precipitation data in? Grids, points, polygons? –  whuber May 28 '11 at 19:32
    
The precipitation data are in grid format –  Kirk May 28 '11 at 20:43
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1 Answer

You could use the Zonal Statistics as Table tool to get the average rain fall value for each city, then you could Join the zonal table to your admin table by a common ID field.

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