topic Re: How to Extract Value from Raster into Polygon? in ArcGIS Spatial Analyst Questions

How to Extract Value from Raster into Polygon?

GwanSeonKim — Thu, 03 Nov 2016 21:09:30 GMT

Hi, GIS users.

I am struggling with extracting value from raster into each polygon.

I have two layers, which are major crop raster and field boundary shapefile.

I attached a picture to explain what I want to do in detail.

Black line shows single polygon for each field boundaries, and yellow and red colors represent corn and soybeans respectively.

Each color includes single pixels (30 by 30 meters).

I want to know how many pixels are located in each field.

I may need to clean (delete) some pixels in raster file since there are many single pixels located in field boundary.

However, I really want to know how may pixels are combined in each field boundary.

Please help me what tools should I used to do that.

Thank you.

Re: How to Extract Value from Raster into Polygon?

DanPatterson_Retired — Thu, 03 Nov 2016 21:13:49 GMT

perhaps Tabulate Area—Help | ArcGIS for Desktop

Re: How to Extract Value from Raster into Polygon?

GwanSeonKim — Fri, 04 Nov 2016 14:27:53 GMT

Thank you for your response.

I tried to use Tabulate area tool, but it takes 12 hours.

I guess it is due to the fact that I have 1290100 field boundaries with 5 different crops.

Do you think is it normal to take this much long?

I also realized that I have so unnecessary polygons if they do not have any pixels.

I additionally asked my question on GeoNet.

Do you have any ideas how to delete those unnecessary polygons?

Thank you again.

Re: How to Extract Value from Raster into Polygon?

DanPatterson_Retired — Fri, 04 Nov 2016 14:32:04 GMT

if you did a tabulate area, what is in the table? There should be a field with results from it, which you can query for polygons that contain output, then switch the selection and save to a file which will only contain the results.

By the way... this is GeoNet...

Also, please answer the question as to what we are looking at... one polygon file... or a polygon and a raster file

Re: How to Extract Value from Raster into Polygon?

GwanSeonKim — Fri, 04 Nov 2016 14:36:39 GMT

I eventually canceled the tabulate area tool because I could not get the output over 12 hours.

Should I wait more? because I do not know whether tabulate area takes this much long or not.

Re: How to Extract Value from Raster into Polygon?

DanPatterson_Retired — Fri, 04 Nov 2016 14:57:37 GMT

cancelling is a good idea

for a circular view ... https://community.esri.com/thread/185407-how-to-deleted-not-matching-polygon#comment-645336

Re: How to Extract Value from Raster into Polygon?

curtvprice — Sun, 06 Nov 2016 01:52:58 GMT

1,290,100 is a very large polygon dataset, and REALLY big for a shapefile. If you're tabulating area I dont' see why single pixels are a problem, you would just get a total for each polygon.

It sounds like you are not sure what you are doing yet. It's generally a bad idea to do a huge overlay until you are sure you are going to get what you want! (Learned this the hard way.)

My advice (once have debugged a processing flow that gives what you want testing with smaller datasets and extent) is to tile your data, that is, do the analysis for smaller groups of polygons, not all million plus at once.

Re: How to Extract Value from Raster into Polygon?

GwanSeonKim — Mon, 07 Nov 2016 14:04:33 GMT

Thank you so much for all of your responses

Re: How to Extract Value from Raster into Polygon?

GwanSeonKim — Mon, 07 Nov 2016 14:20:29 GMT

Hi,

First of all, thanks for your response.

I have Cropland Data Layer, which is 30*30 meter satellite image.

I want to make a field-based panel data in order to see the crop rotation for specific crops in Kentucky at the end.

First, I was thinking to figure out how many fields are growing corn, soybean, and so on based on field boundary shapefile.

Since I have so many unnecessary fields (i.e., not for corn or soybean), I would like to delete those fields. (It is because

Second, I want to calculate how many pixels are located in each field in order to calculate total acres in each field based on number of pixels.

Based on your suggestion, I may able to test smaller datasets and extent. However, I have 92 counties based on field boundary shapefile. It means I need to repeat 92 times.

If you have better ideas, please let me know.

Re: How to Extract Value from Raster into Polygon?

curtvprice — Mon, 07 Nov 2016 14:42:49 GMT

> It means I need to repeat 92 times.

Exactly my suggestion. This will probably run much faster than running the whole thing at once due to memory limitations. Looping or model builder iteration should make this pretty straightforward.

Re: How to Extract Value from Raster into Polygon?

MaribethPrice — Thu, 10 Nov 2016 21:39:23 GMT

You might also try the Zonal Statistics as Table tool, with your polygons as the zone data set and the crop raster as the values data set. It will provide a table with a Count field for all the pixels in each polygon.

You would need to reclasify (Reclassify tool) the raster so that you would have only corn or only soybeans in each raster. Give each a value of 1 and a nodata everywhere else.

The output is a table that you would join back to the polygons. You will need a unique identifer for each field; the ObjectID should work if you don't have anything else.

You will need a Spatial Analyst extension license to run these tools.

Maribeth

Re: How to Extract Value from Raster into Polygon?

GwanSeonKim — Mon, 14 Nov 2016 16:00:25 GMT

Thank you for your response.

I have one more question to you.

I have a raster file, which is soil map.

In the raster, there are so many columns, but I just want to use one column named "slope" and use zonal statistics tool.

However, I do not know how to select only one column in the raster.

I tried to run the zonal statistics, but I could not figure out what those values are.

Please let me know if you have any ideas,

Sun

Re: How to Extract Value from Raster into Polygon?

MaribethPrice — Mon, 14 Nov 2016 18:30:21 GMT

Sun,

Rasters only store ONE field attribute directly and it is contained in the “Value” field. Any other fields may have been added by users or copied during a polygon-to-raster conversion process. Most raster tools use the Value field by default, and not many of them allow you to select an alternate.

If you have a soil raster, then I surmise that the Value field contains a unique number code for each soil unit, and the slope field you indicate was merely copied from a polygon soils data set when it was converted to the raster. Presumably this field already contains the average slope of the field, so if you trust this value, then you don’t need to run zonal stats at all.

To use zonal stats, you need a slope raster containing slope values in the Value field (not a soils raster containing a soil code). If you have a digital elevation model already, you can calculate slope from the DEM quite easily with the Slope tool and use that in zonal stats.

You might want to review the Help files on how rasters are stored and analyzed; it sounds like you have might some misunderstandings about how they function.

Maribeth

Re: How to Extract Value from Raster into Polygon?

GwanSeonKim — Mon, 14 Nov 2016 19:30:43 GMT

Maribeth,

I guess I did not have enough knowledge about the raster.

Now I understand what is your point, and I figured it out.

The value in raster is uniquely assigned to each observation.

Once I use zonal statistical tool, then I can join with other fields based on the value.

Thank you so much.

Re: How to Extract Value from Raster into Polygon?

GwanSeonKim — Tue, 15 Nov 2016 14:18:22 GMT

Maribeth,

This is Sun again.

I am sorry to ask you many questions.

Today, I tried to run zonal statistics as table tool again, but the tool does not work.

I did exactly same steps with same files, but I could not get the output.

For example, it took 10 mins to get output yesterday, but the tool is running more than an hour without output.

Do you have any ideas why I have this issue?

Thank you.

Sun