Extracting data from Raster landcover map, per polygon

[BrianMubiwa]

Hello Colleagues,
I hope you can assist me. I have just created a land-use/cover map. Now I want to obtain the share of the different land-use/cover types within each polygon. I have tried actually extracting polygon by polygon then get the percentages but this is tedious as I have more than 100 polygons. Is there a model/which model can I use to obtain such information in an automated way?

Many Thanks

[GregoryLipps]

I don't know if you'll be doing a lot of this sort of thing, but if so, you should invest the time into downloading, installing, and learning the Geospatial Modelling Environment (spatialecology.com), which has replaced Hawth's Tools. 

The particular function that does exactly what you want is isectpolyrst  (Intersect Polygon with Raster).  It replaces the Thematic Raster Summary of the old Hawth's tools.

Greg

[MatthewReetz]

Greg's solution is perfect.  It takes a little bit of time to install GME and the required components (R, Statconn) but once you get those running the GME environment was pretty straightforward and I got this to work quickly.  It even allows you to do a proportion analysis so you don't have to do any work in Excel.  I spend days on this the other way and this was super fast.  Then you simply can load your target shapefiles and the landcover proportion data are included in the attribute table.

Here's the download instructions for GME.  Follow them to the letter.  http://www.spatialecology.com/gme/gmedownload.htm.  The only snag I ran into was that I initially had the program files saved in x86 program files so GME didn't link to R.  Install both the 32 and 64-bit versions of R.  But, save everything to your basic program files folder if you are indeed on a 64-bit system.

[EricRice]

Greetings Matthew,

If you just want to use ArcGIS an not bother with 3rd party items, you can simply use the Zonal Histogram tool which enables you to investigate the frequency distribution of values in one dataset (your LULC raster)  within classes of another dataset (your polygons). Here is an overview of the zonal toolset.  There may be other tools that are of interest for your analysis.

Regards,
Eric

[MatthewReetz]

Thanks Eric,
    But (and correct me if I'm wrong), that only gives you a summary breakdown for all of your polygons put together.  What we needed was something that gives you the breakdown of raster cell types for each individual polygon, which is what GME does, and then puts those data right into your shapefile so they can be easily exported for data analysis.

[EricRice]

Hi Matthew,

Zonal Histogram does not summarize the raster using all the polygons as one item.  It operates on each unique zone.  A zone is defined as all areas in the input that have the same value. The areas do not have to be contiguous.  If each polygon has a unique ID though, then it gives you what your looking for in the sense that each polygon will define the area being summarized.  If you have overlapping zones, the you should use the Iterate Feature Selection iterator and collate the results.

Best Regards,
Eric