topic Re: ArcGis Pro Zonal statistics as table in ArcGIS Spatial Analyst Questions

ArcGis Pro Zonal statistics as table

Hope-Hauptman — Mon, 19 Jul 2021 17:33:54 GMT

I have a soil classification raster that I clipped to a 500m radius circle around central contamination points. I am trying to determine the majority soil type (hydrologic group) in the clipped rasters using the Zonal statistics as table tool but I must be doing something wrong?

I have done this successfully with another raster but there was only one value in the attribute table to calculate the majority within the clip, here there are a more than one column in the attribute table.

For example in the picture - visually most of the buffer zones seem to have a majority blue by area (soil type B) but I would like ESRI to calculate the majority area for each circle for me...

Re: ArcGis Pro Zonal statistics as table

curtvprice — Mon, 19 Jul 2021 17:37:57 GMT

Your buffers overlap. To get correct results you need to run the Zonal Statistics (or Tabulate Area would be better so you can see more detail) tool for each circle one at a time; you could do this using modelbuilder or python iteration. There are some development efforts to avoid the overlap problem but since this is a small number I would just do the buffers one by one.

Moving this to the Spatial Analyst space where lots of smart people may have more suggestions.

Re: ArcGis Pro Zonal statistics as table

Hope-Hauptman — Mon, 19 Jul 2021 17:37:37 GMT

This is just a small picture. I have thousands of clips.

Re: ArcGis Pro Zonal statistics as table

curtvprice — Mon, 19 Jul 2021 18:32:43 GMT

I did build a tool to Weed Points (NACT) so you can do them in groups. But, I looked in the help and at ArcGIS Pro version 2.8 (but not ArcMap 10.8, unfortunately), Zonal Statistics As Table handles overlapping polygons. How wonderful!

I re-read your question. If the value is in another field in the raster table besides Value, you can create a new raster of the table value you want using the Lookup tool.

Re: ArcGis Pro Zonal statistics as table

JayantaPoddar — Mon, 19 Jul 2021 18:21:02 GMT

A few check-points. Please verify

1. Use the buffer polygon layer as Input Feature Zone Data. For the Zone Field, use a field of unique values like "ObjectID". Ensure no "Buffer" polygon Feature part is selected in the map.

*EDIT: Ensure there are no multipart feature in the Buffer layer. While creating the buffer from the points, the Dissolve Type parameter should be "No Dissolve".

2. For input value Raster, you may use the clipped raster (or even better, the full Raster).

3. For Statistics Type, check with "MAJORITY"

Re: ArcGis Pro Zonal statistics as table

Hope-Hauptman — Mon, 19 Jul 2021 18:30:14 GMT

Yes check on all those boxes. I tried it again using the full raster as the input raster but instead of the majority soil hydrologic group as the majority group I get an area number for the majority? See pic.

Re: ArcGis Pro Zonal statistics as table

curtvprice — Mon, 19 Jul 2021 18:46:02 GMT

Rasters are stored and manipulated as numbers not text. So to get the value in the table you probably need to do a join (Join Field is probably the easiest way to do this) to copy the hydro group value over to the table from the input raster table (Value being the join field).

Another thing to look out for is that the majority is not necessarily a plurality, that is if a buffer has enough hydro groups, you may want to use the Tabulate Area tool instead so you can see those special cases and deal with them. This will involve a little more database work on the output, but I think it is probably worth it.

Re: ArcGis Pro Zonal statistics as table

curtvprice — Mon, 19 Jul 2021 18:47:58 GMT

One more thing this hydro groups are categories and if your interest is to look at well risk, this may be best handled for this analysis by converting the cell values to a vulnerability score (say 1-10) and doing an average instead of picking the majority. Just a thought.

Re: ArcGis Pro Zonal statistics as table

Hope-Hauptman — Mon, 19 Jul 2021 18:58:42 GMT

Thank you - I did successfully use the tabulate area tool but I don't really need the majority area I want the majority soil class. I know I can than add field and calculate the maximum value in each object ID but since i need the category and not the number this isn't really helpful. I hope that makes sense. Like for example in the tabulate screenshot for object ID 1: soil class D has the maximum value in the first row. Bout I don't care about the numerical value - I just need to know that object ID 1 majority is soil class D and so on for the other objects. I did do this for another raster but there was only one value and it was categorical - landuse type.

I wanted to share the data but it is too large of a file to upload...

Re: ArcGis Pro Zonal statistics as table

curtvprice — Mon, 19 Jul 2021 19:16:55 GMT

You can find this out using a calculate field expression to find out which field matches the maximum value row by row. You would do this with a python code block with the Calculate Field tool, or dump the table and do it in excel and do it there. If the row by row max of the fields is equal to the column you want, that's the answer, so you can use if statements to identify which is the plurality. And maybe another to tag whether it is the majority.

Again, what are you trying to accomplish with this?

Note there are also some nice SSURGO raster layers in ArcGIS Online that have derived soil properties that can be averaged to get a value not susceptible to the plurality/majority problem. For example see Drainage Class.

Re: ArcGis Pro Zonal statistics as table

curtvprice — Mon, 19 Jul 2021 21:09:36 GMT

> I did do this for another raster but there was only one value and it was categorical - landuse type.

If you want to do it that way, the solution is to use the Reclassify tool to convert your soil types into integer codes (1,2,3,4..) (like your land use codes were), do your zonal statistics as table to find majority value, and then map the results (1,2,3,4..) back to soil codes using an expression or lookup table.

I know this seems unwieldy but is because ArcGIS rasters do not store text, they store integer or float numbers, so to do calculations on categorical data the values must be integer, not text codes like "A/B".

Re: ArcGis Pro Zonal statistics as table

Hope-Hauptman — Mon, 19 Jul 2021 20:27:25 GMT

Unfortunately I don't know how to write python code. The drainage class looks promising - I will give it a try. Thank you very much.

Again, what are you trying to accomplish with this?

- Sorry I did not see this earlier. Well, I am just doing an initial data analysis but I want to understand if there is a positive correlation between well contamination concentration (around a zone of interest) and soil type.

Re: ArcGis Pro Zonal statistics as table

JayantaPoddar — Mon, 19 Jul 2021 21:47:20 GMT

Something is missing. How is your current requirement different from ArcGIS Pro determine dominant land use type around each point in a given area (500m buffer) that you posted last month?

Re: ArcGis Pro Zonal statistics as table

curtvprice — Mon, 19 Jul 2021 21:57:26 GMT

Jayanta, the difference is now the input zone values are text, not integer (see my previous post). The land use codes were integers (Value field), the soil type values are in a text field in the raster table.

Re: ArcGis Pro Zonal statistics as table

Hope-Hauptman — Mon, 19 Jul 2021 22:05:08 GMT

Great question. Last month I also used Zonal Statistics as Table tool to calculate majority land use but the VALUE field was the land use code (see screenshot last month). Now with my current problem the VALUE field is not what I want to calculate my statistics on. I want hydrologic soil class. Do I need to title it VALUE instead? Another suggestion was to use the lookup tool but that did not work... Not sure what I am doing wrong. Sorry I know this is a repetitive question and I thought I had this problem solved last month...

Re: ArcGis Pro Zonal statistics as table

JayantaPoddar — Mon, 19 Jul 2021 22:25:38 GMT

I don't have a similar data to test. Could you add just the buffer layer and the Clipped Raster layer on map, and create a map package? Share the map package through a Google Drive, Dropbox or FTP link.

Let me have a look at the data.

Re: ArcGis Pro Zonal statistics as table

curtvprice — Mon, 19 Jul 2021 22:36:51 GMT

Remember, you can only do statistics on number codes not text codes, that is the root of your issue.

When I look at your raster I think the easiest approach is to use the Lookup tool with your raster as input, and specify the text field HYDROLGRP_DCD. This output raster from the Lookup tool will have a unique Value field (an integer) and your text field in it. Run your Zonal Stats As Table on this using the Value field. Then you'll have the majority soil code (as the Value integer). To add the soil text code to the zonal stats table, use the Join Field tool with your zonal output as the input table, input field Value, the raster table (with Value and HYDROLGRP_DCD) as the join table, join field MAJORITY. This will add your soil codes into your zonal stats results.

Re: ArcGis Pro Zonal statistics as table

Hope-Hauptman — Mon, 19 Jul 2021 22:36:41 GMT

You are a wonderful person. I cant thank you enough - I've wasted hours on this. I almost want to edit my original question so that others struggling with this can benefit. Have a great day.

Re: ArcGis Pro Zonal statistics as table

curtvprice — Mon, 19 Jul 2021 22:39:58 GMT

But you CAN edit your question! But it is good etiquette to add info in an UPDATE block to preserve the context of the responses to the thread. Not time wasted, you have learned a lot about Spatial Analyst and rasters today!