topic Re: Extracting raster values using buffers in ArcGIS Spatial Analyst Questions

Extracting raster values using buffers

MoaraMartins — Mon, 25 Jun 2012 15:15:22 GMT

Hi,

I am trying to extract values from a raster using a buffer and it is not working. I am using Arcmap 10 and I have been trying to accomplish that task using Zonal statistics as table. I have 1166 records on my buffer table and when I perform the extract I only get three rows on my table.

I would appreciate any suggestion someone could offer to get that fixed.

Thank you

Re: Extracting raster values using buffers

EricRice — Mon, 25 Jun 2012 16:58:00 GMT

Greetings,

Do the buffer polygons overlap each other? They are converted to raster internally which means overlap is not possible in raster form - a pixel can only be 1 value. The only other thing I can think of is that the polygons are really small relative to the resolution of the raster being sampled. For overlapping polygons you need to iterate through each feature and process them individually. Be sure to set your snap raster and cell size in the environments.

Best Regards,
Eric

Re: Extracting raster values using buffers

MoaraMartins — Mon, 25 Jun 2012 17:58:15 GMT

Hey Eric,

My raster file is a MODIS img and my buffer file was created from a point dataset. I want to get the values of the raster cells within the buffer and it is not working at all...

Thanks

Re: Extracting raster values using buffers

DarrenWiens2 — Mon, 25 Jun 2012 18:44:44 GMT

From the help:

If the zone feature input has overlapping polygons, the zonal analysis will not be performed for each individual polygon. Since the feature input is converted to a raster, each location can only have one value.

An alternative method is to process the zonal statistics iteratively for each of the polygon zones and collate the results.

If you're comfortable with python, you should be able to cycle through each buffer with a SearchCursor, use Make Feature Layer with the appropriate where clause to pull out each buffer one by one, calculate statistics using Zonal Statistics as Table, and Merge all the tables together.