I've discovered a weird phenomenon using zonal statistics with a colleague at another office. We are attempting to use the Zonal Statistics as Table tool to sum the value of raster cells within polygon zones. We are using two zone polygon files: one with about 12 "discrete" zone polygons, and the other with a single "broad" zone polygon.

The odd result is this: While we get the same results running the raster and discrete zones polygon file, we get different results when running the raster and broad zone polygon file - by an order of magnitude (for example, where one result is about 50 million for me, his is about 5 million).

We are using the same raster, and the vector files have been projected to match the raster projected coordinate system exactly - to avoid issues from projecting on the fly. The only difference we can find between our protocols is that he is on ArcGis 10.1 and I am on Arc 10.2.1. As far as I know we both have all licenses.

From @Whuber's detailed explanation at Does Zonal Statistics value change when applied on subset of data using ArcGIS Spatal Analyst?, I think it has something to do with changes in the "black box" of zonal statistics calculations.

  • I edited it to correct my original statement - my colleague is working in 10.1, not 10.0. – SharonB Sep 16 '14 at 17:38
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    I know this is simple but the order of magnitude thing makes me think of something. Has the person with the lower number expanded the column in the attribute table (make it bigger left to right) to see all the digits. Arc does not auto-adjust the column width and I often see students give me answer like 5,000,000 instead of 50,000,000 as they have not expanded the column. – If you do not know- just GIS Sep 16 '14 at 18:39
  • user two seven two three nine - you win! You can make your comment an "answer" if you'd like. I hadn't had a chance to close up this question. In talking through the steps my colleague realized the column wasn't expanded exactly as you said. – SharonB Sep 16 '14 at 19:41
up vote 1 down vote accepted

I know this is simple but the order of magnitude thing makes me think of something. Has the person with the lower number expanded the column in the attribute table (make it bigger left to right) to see all the digits. Arc does not auto-adjust the column width and I often see students give me answer like 5,000,000 instead of 50,000,000 as they have not expanded the column.

  • Although the answer is super simple, I'd take this opportunity to note that in working with this less-Arc-experienced colleague, it was a reminder that newer Arc users get tangled in the little non-spatial nonsense, and so walking through steps together one at a time can be a really valuable way to find kinks in the process. – SharonB Sep 17 '14 at 18:37

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