I have a park polygons layer and a set of points which I gave a 1000m buffer. For each of them I had calculated the area size with calculate geometry. So with which tool could I calculate the size of park within each buffer? I had tried intersect; it gives the results of the size of many parts of polygon under the buffer, I need to calculate the area size by myself. If I have 20 buffers could I get the sum of the polygons' size directly? I am using ArcGIS.
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.
If I understand you correctly I think you are looking for the clip tool. in ArcGIS 10 and above it should be in geoprocessing → clip (or in toolbox Toolboxes\System Toolboxes\Analysis Tools.tbx\Extract\Clip)
your input would be the parks and the clip feature would be the buffer. this will create a new feature class that is only the parts of the parks that are within the buffer. from there you can calculate the geometry again and you should have your answer.
** you may want to dissolve your buffers first to remove any overlap. geoprocessing → dissolve.
This really gave me fits because I had a similar problem. I thought that intersect resolved my issue, but upon closer inspection I realized that intersect did not "count" my polygons (also woods/trees) that extended beyond the area of my buffer zone (i.e. sq ft for big wooded areas was computed as zero). On the other hand, other strategies I had tried resulted in the computation of the WHOLE wooded area without regard to my buffer zone (e.g. resulting in a computation of wooded area that was greater than the area of my buffer zone). So I either ended up with data that didn't count big wooded areas at all or counted the whole wooded area despite my intent to only count what portion fell in the buffer zone. Here's what finally worked for me:
Clip the tree layer w buffer zones
Intersect Clipped tree canopy files with buffer zones (This step connects the clipped data back to the school ID / buffer zone)
Use dissolve based on the ID of your buffer zone (mine was school ID) - input the Clip-intersection layer and check only the school ID so that it aggregates by school.
Open the dissolve attribute table; create new field (long integer) and use calculate geometry to compute square feet for total tree canopy falling within each buffer zone. Use that total sq feet and divide by the total area of the buffer zone to create a proportion of tree canopy. Export that data for use in statistical analysis.