Drawing by Aaron Westerberg, Graphite on Vellum, (the photo is an Edward Cutis photograph.)
Here’s a excerpt from an Aaron Westerberg step by step which shows how he begins with a basic notan (two large interlocking values representing light and shadow.) He writes, "This is one way I draw. I started with the right eye and measured everything from there. Keeping everything just two values I preceded to block in the rest of the head. this is the mapping stage I am lining everything up. Once everything is placed correctly I proceed to a full value drawing. [Darks first!] The half tones in the light were done last and were very easy once all the darks had been inserted. This is a fun way to draw."
This is very similar to our notan process which you can learn about here:
http://www.smartermarx.com/t/portrait-notan-exercises/437/3
You can learn more about Aaron’s work here: https://aaronwesterberg.com/