Use the Polygon tool to trace over the site. Make sure that you create a closed shape.
Counting Site Areas (Impermeable Surface). By now you might be able to figure out how I’m going to do this one. I need a polygon for the site area and I need areas for the buildings and impermeable surfaces. You Can name objects, as I did in the Introduction to Worksheets. That works OK when you have one or two objects, but when the projects get more complex, than method does not work.