extracting information from a Raster landuse file by a polygon shape file

Question

I am in desperate need of help.  I have obtained a raster landuse file (.tif) from USDA website for Ohio and need to extract information from it using a polygon shapefile I have created that entails some study sites with a 1km buffer.  Ultimately, I would like to obtain the percent landuse within my buffer polygon shapefile but the program is not letting me.  I have tried several routes including Spatial Analyst tools and even trying to convert my raster file to a polygon file for clipping.  I need to do these analyses for my Master's thesis so there is no avoiding figuring it out.  ANY help or suggestions would be greatly appreciated!!

RebeccaCunniffe · Answer

These threads should get you going, but the main thing I will point out is that Spatial Analyst doesn't calculate percentages for you.  It gives you the raw counts.  You must convert to percentages.  I should also point out that if your buffers overlap you must handle this special case by looping through the features individually.

http://forums.arcgis.com/threads/70779-ArcMap-Land-use-type-as-a-percentage-of-total-area?p=248229#post248229

http://forums.arcgis.com/threads/31789-Calculating-the-area-and-the-percent-of-cells-of-each-value-in-a-raster!-Automaticall?p=236867#post236867
(I have a GPK in this one that shows how to convert counts into percentages)

Best,
Eric

Hi Eric,

In your above reply you mention that for overlapping buffers one must loop through the features individually. I have tried to search for how to do this, but have not had a lot of luck (I am still quite a novice in GIS). Would this involve using code?

I have a large number of circular buffers and wish to extract the total area of the buildings within each buffer, from the building shapefiles that I have. Every buffer overlaps with the next, so the intersect function has not worked, and I likely have to do what you suggested, but I am just not sure how. If you have any suggestions, or links to other threads that might explain how to do this, I would appreciate it a lot.

Thank you,

Rebecca

Buffer example.jpg

EricRice · Answer

These threads should get you going, but the main thing I will point out is that Spatial Analyst doesn't calculate percentages for you.  It gives you the raw counts.  You must convert to percentages.  I should also point out that if your buffers overlap you must handle this special case by looping through the features individually.

http://forums.arcgis.com/threads/70779-ArcMap-Land-use-type-as-a-percentage-of-total-area?p=248229#post248229

http://forums.arcgis.com/threads/31789-Calculating-the-area-and-the-percent-of-cells-of-each-value-in-a-raster!-Automaticall?p=236867#post236867
(I have a GPK in this one that shows how to convert counts into percentages)

Best,
Eric