I've created 2km buffers around 108 points and clipped habitat maps to these buffers, as per instructions given. I now need to calculate the area of each polygon of each habitat type within each buffer and I've very lost on how to do this.
When I clipped the habitat map to the buffers the attribute table produced gave the area of each individual polygon (all >2000 of them) but there's no field in the table to say which buffer the polygons belong to and I cannot think of a way to add a field like this in.
I've tried summary statistics to get the area but this gives total area from all buffers when I need the areas for the habitats within each buffer.
My supervisor told me to add an additional field to each layer file and the ‘calculate geometry’ function to calculate the area for each habitat type within each buffer. However, I can't add the names of the habitats as fields to the table as the names are too long. When I shortened the names and tried this, it calculated an area for all the habitats, not just the habitat in the field heading.
The other suggestion was to use the Tabulate Areas function of the Spatial Analyst extension in Arcview to calculate the area of each buffer occupied by the habitats it overlapped with – however, I don't have this extension so I can't do this.
Best Answer
If you had an advanced license, you could simply use the Tabulate Intersection tool.
Without it:
1) Buffer the points. Do not select the option to dissolve the buffers; otherwise, they won't retain the identifying attributes of the original points.
2) Instead of using the Clip tool, you need to use the Intersect tool. The output of this tool retains all the fields from both inputs. In this case, intersect the buffers and the habitat; the output features will have all the same fields as the buffers and the habitat. It even handles situations in which buffers may overlap by duplicating the records from the habitat data, as needed.
3) Dissolve the result of the intersection based on whatever unique identifying field(s) you have for both the points and the habitats. So, in the "dissolve fields" box, you would select something like "Point_Name" and "Habitat_Type".
4) To the output of the dissolve, add a new field to store the area and calculate its geometry.