Count the area of rasterdata in specific shapefile polygons (residential density in different districts)

Question

I'd like to count the exact area of three different residential classes (low, medium, high) by district of a shapefile which contains 225 districts. like: district 1 has: XXX sqm low, XXX sqm medium, XXX sqm high. distict 2 has: XXX....

the residential classes are a file system raster, the districs are one shapefile.

I can count the total area of the residential classes of the whole study area. but I can't count the area for every unique district I have in the shapefile. (Maybe I could count the area for 1-3 specific districts I pick but for 225 it would be too time-consuming) After all I'd like to see the area of each district in the attribute table of the district-shapefile and be able to export the data to Excel. I hope you can help, thanks.

Answer 1

Sounds like you have access to Spatial Analyst extension. Tabulate Area should do the trick, but you do need to be mindful of overlapping zones (e.g. districts).

http://resources.arcgis.com/en/help/main/10.2/index.html#//009z000000w2000000

Answer 2

You can use the Tabulate Area tool to do the job. Use the following steps to get the values for all 255 districts (or any number you might have):

1) If your district polygon shape file does not have a unique Identifier for each feature in the attribute table, then add it, i.e. add a new field named Id (or any other name) and calculate Id = FID + 1. The unique field will be needed later on in step 3.

2) Run the Tabulate Area (Spatial Analyst) and use your district polygon as "Input raster or feature zone data". The tool will create a table with the areas of each classes that fall into each district and load it to ArcMap.

3) Then right click on your district shape file and select Joins and Relates and "Join attributes from a table", choose an Id field added in point 1, then select the table created in 2 and then a Rowid or ID - this will add the results obtained in point 2 to the district shape file - JOB DONE! To make the Join permanent export the district shapefile to a new shapefile - you can then organize your field names, etc. if needed

Hope that helps!

meryloo