arcgis-desktopbufferfield-calculatormodelbuilder
In one Shapefile I have created 1200 buffer zones Around coordinates. I created a field and calculated the buffer zones area in hectares.
Then I clipped different landcover layers to the buffer zones.
Now I want to calculate How many hectares of eg. Forest there are in Each buffer zone And afterwords the amount of felds, And so on.
The calculations shall be done in ModelBuilder.
Can anybody help?
If you're using ArcGIS 10, you can do it without Editor or Info by creating the buffer as a different layer, then doing a Union (Analysis->Overlay) on the initial layer and the buffer. This should create additional fields in the dataset, for instance if the unique field is "Name", then there should be a field "Name_1". In other words the union is basically joins the structure of both layers together.
You can then filter out all shapes where "Name" is nothing (Deifinition Query = "Name"<>'') [two single quote marks after <>] which should leave you with just the initial shapes, split by the buffers.
You can then calculate the area of each of these objects into a new field and do a spatial join on the buffer layer counting the sum of the area of the filtered Union Layer.
Hopefully this graphic illustrates this visually.
I can think of a couple of approaches to this. The simplest one is to calculate the difference between your buffers and the envelope of your area of interest. Have a look at the Erase and Symmetrical Difference Tools in the Analysis Toolbox. Your problem here though, is that they are available only with the ArcInfo licence. ETGeoTools might have something but I don't recall any useful function in the free version. QGIS can accomplish the task for free though.
A simple work-around for ArcGIS if you don't have the ArcInfo licence, is to create your envelope polygon and then Union it with your buffers. From the result of that operation, select all the polygons that are identical to you buffer areas and delete them. Everything left is your "inverted buffers".
Best Answer
You can use the Intersect tool to intersect your land cover layers with your buffer layer. You can then recalculate the areas of each land cover layer within each buffer.