I have read that to create a buffer within a line or polygon, use a negative number for the unit (e.g. -100 meters). However, in ArcMap 10.2 this is not allowed or in my experience it creates an error. I have a an area either polygon or polyline (I have created both to attempt the buffer) that I would like to have a 100 meter buffer within the boundary ONLY. When I create the buffer from the line example, it is 100 meters on each side (inside the line and outside the line; I only want inside) and when I create the buffer from the polygon example it buffers everything within the feature. Suggestions? I apologize if this has been mentioned before, I did not find it while searching for an answer.