bufferpolygonqgis
I have a point shapefile of villages where data was collected in Northern Kenya. I created a buffer around those villages.
The second vector layer contains polygons defining areas according to vegetation type. So for example, a forest might be surrounded by a narrow ring of woodland in an area which is mainly grassland. I'm trying to obtain a percentage of each vegetation type within the buffer per village.
I'm using QGIS 1.7
There are a couple ways to accomplish this task. The first is the Summary Statistics, as I explained in your other question. A second way to do this is to first perform your Intersect, and proceed this with a Dissolve, with the buffer unique ID field as your Dissolve field.
This creates a new feature class with each feature representing all buffer-areas-within-parks.
You can use the QGIS Zonal Statistics Plugin to summarize raster data within vector features. The plugin writes the statistics to the vector layer. To export the shapefile attributes to csv format, do the following in QGIS:
right click layer > Save As... > Comma Separated Value [CSV]
From the plugin documentation:
With the icon_zonal_statistics Zonal statistics plugin, you can analyze the results of a thematic classification. It allows you to calculate several values of the pixels of a raster layer with the help of a polygonal vector layer (see figure_zonal_statistics). You can calculate the sum, the mean value and the total count of the pixels that are within a polygon. The plugin generates output columns in the vector layer with a user-defined prefix.
Best Answer
You can use the "Intersect" tool on the buffer and land use layers. This should create a third layer where buffers are "cut out of" the land use polygons. Then you can calculate the area of the resulting polygons using Field Calculator.
Village buffer before
and after the Intersect operation and calculation of area using Field Calculator:
Divide by the total area of the buffer to obtain percentage values.