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I am doing a ArcGIS raster project. Now I am at the step where I already created a scoring system for my targeted area and I assigned the score to each of the cells in side the targeted area, as shown in the picture below Score of the cells inside targeted area

Now if I want to find the average value of the cells of each region group.

What tool shall I use?

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To do this, you need a separate raster where each group has a unique value (ie, each cell within a group shares the same value and no other cells have that value). If you do not have this already, you can create it with the region group tool.

One thing I noticed from your screenshot is that there are some pixels that are not part of any of the large groups. Each of these pixels will become their own regions in the output. Likewise, any of the groups that are not completely contiguous will be broken into multiple regions.

Once you are happy with your region group raster, use the zonal statistics tool to calculate the mean of each region group. The raster you showed above will be your value raster input and your region group raster will be your zone raster input. Statistics type should be mean (or whatever other statistics you want to calculate for your groups).

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  • Thank you so much for your timely reply. This is exactly where I am stumped. I am doing Region Group after assigning each of these pixels values. Now it seems that every color stripe is their own group, which is the last thing I wanna see happen. Shall I region group it beforehand and then assign the value? BTW, how shall I clean out all these small pixels? Focal statistics with major?
    – Bowen Liu
    Commented Aug 5, 2016 at 20:06
  • For the zone grouping method, are you using within or cross? I think you need to use cross. When you use cross, you also need to set the excluded value parameter to whatever your background value is. (The white in the image above.)
    – Christopher
    Commented Aug 5, 2016 at 20:15
  • What if it's nodata? The white area in the picture. And what is the purpose of using cross instead of within? Thanks again
    – Bowen Liu
    Commented Aug 5, 2016 at 20:18
  • Within checks to see if pixels are contiguous and have the same values when defining groups. Cross only requires that pixels are contiguous. Try entering nodata or null as the excluded value to see if it will accept it. If not, you could reclassify the raster and change nodata to some other value.
    – Christopher
    Commented Aug 5, 2016 at 20:28
  • Alternatively, I believe that zonal statistics will also accept a polygon feature class to define zones. This would also make it easy to get rid of pixel noise. This may be a quicker option than region group if you used a polygon file to create the raster above.
    – Christopher
    Commented Aug 5, 2016 at 20:31

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