Drawing with a pen or pencil implies an idea exists and one is manifesting it on paper. Subtractive "drawing" is a great technique to create space without having a preconceived idea of the form. Below are photos of my conceptual subtractive section of my studio project, a center for sleep disorders. The act of erasing creates a nice after effect on the paper and helps flush out spatial ideas and building circulation.
Click on the first photo to cycle through them
“An architect's most useful tools are an eraser at the drafting board, and a wrecking bar at the site.”
- Frank Lloyd Wright