# Calculating coverage of vector polygon over other polygons?

I have a shapefile file that contains a LiDAR footprint and I'm trying to figure out how much a county is covered by the LiDAR footprint. Two separate shapefiles. The attribute table for the county layer is separated by counties with an area. The LiDAR footprint is one large footprint that covers multiple counties.

• Try to use Intersect Tool to find the intersection of two layers – Farid Cheraghi Mar 4 '15 at 1:01
• Ok, then what do I do next? How do I calculate the area covered for each county? – Christopher Harrod Mar 4 '15 at 1:10

## 1 Answer

Intersect, identity and union are the three main overlay functions that could be used in this instance.

For the simplest case how many square metres (feet, inches, miles..) of LiDAR coverage are in each county?:

Using Intersect overlay the LiDAR coverage over the counties shape file, calculate the areas to a field and then summarize with Summary Statistics with statistics field of Calculated areas, type SUM and Case field of county name, this will give you a table of each unique county name and how much coverage (in area units).

More complicated How much of this coverage is over each county?:

For percentage of LiDAR coverage in each county you must first know the original area of the LiDAR coverage, add a field called Initial_Area and then calculate that (make sure your units are the same), then do the intersect with the county shapes, calculate the individual areas and do the summary again but include Original_Area as a Case field (they should all be the same so it wont muck with the tabulation) then add a field (percent) and Calcuate Field using the calculation `(Intersect_Area / Initial_Area) * 100` on the summary table will calculate the percentage of LiDAR strip for each county by name.

• Thank you, I will try when I'm back in the office Friday and leave feedback if it works. I appreciate it. – Christopher Harrod Mar 4 '15 at 21:43