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Extract raster values using overlaying polygons

CarlosBecker

Dear all,

I???ve been trying to calculate average raster values for a set of overlaying polygons and have no idea how to do this. I asked a bunch of people, tried different approaches (converting raster to points, etc???), but still can???t do when polygons overlap. My polygon layer (species geographic ranges) consists of several polygons that overlap in space. I intend to calculate average vegetation density for each polygon using a vegetation density raster.

Can anyone help me get onto the right path?

Thanks a lot

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DonovanCameron

You could try the Extract by Polygon (Spatial Analyst) tool to get the cells from the raster that would intersect your polygon.

Then on the new raster run a Summary Statistics (Analysis) to get the Mean of the cells in the raster.

EricRice

Do you want a raster that represents the average or do you want the average value to be an attribute of the polygon? Most of the time its the latter. I would point you to the Zonal Statistics as Table tool in Spatial Analyst. You should check out this thread, where I uploaded a snapshot of the model I used to do this.

Regards,
Eric

CarlosBecker

Dear Eric and Donovan,
Thanks for helping me, it worked!!!

I needed the average raster value to be an attribute of the polygon, so I used Zonal Statistics as Table tool in Spatial Analyst as Eric pointed out. It performed perfectly when I selected a subset of species (about 100 species, which means more or less 600 polygons). When I run for all species together it doesn't calculate for all polygons. I�??m afraid it is because of the overlaps. Thanks a lot for taking your time; any additional thoughts are welcome.

Thanks guys,
All the best.

Gui

PS. Donovan, I tried "extraction by polygons" but I wasn't able to find a way to add a polygon layer, only to enter x,y coordinates for one polygon only. Am I missing something here? Thanks a lot.

DonovanCameron

PS. Donovan, I tried "extraction by polygons" but I wasn't able to find a way to add a polygon layer, only to enter x,y coordinates for one polygon only. Am I missing something here? Thanks a lot.

What the input is asking for is to add ALL the polygon vertices from an individual polygon or the merging of a few, with the last vertex entered to be the same as the first to close the loop.

Alternatively, you may have more luck using the Extract by Mask tool.

CarlosBecker

Thanks Donovan,
I'll try it tomorrow.

MelisaBernard

I just completed something similar using Geospatial Modelling Environment toolbar (formerly Hawth's Tools). Perhaps an option you may want to investigate? www.spatialecology.com for more info. The command I used was "isectpolyrst."

minanasr

Hi,
I am working with a polygon layers with a lot of nested and overlapped polygons. I have used isectpolyrst for area and proportion calculations and it worked perfectly but to extract a value of floating raster it doesn't work. in fact it produces fields with NoData values (-2147483648) for averages. I made sure the projections of my raster and polygon layer are the same but still no luck.
Anybody could give me some recommendation on this?
Thanks

AndyBell2

Hi,
I am working with a polygon layers with a lot of nested and overlapped polygons. I have used isectpolyrst for area and proportion calculations and it worked perfectly but to extract a value of floating raster it doesn't work. in fact it produces fields with NoData values (-2147483648) for averages. I made sure the projections of my raster and polygon layer are the same but still no luck.
Anybody could give me some recommendation on this?
Thanks

Did you ever figure out the issue? I am dealing with same problem.

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