illustration - What is this circle technique called?

What is this technique called:

http://dribbble.com/shots/260469-Squirrel-Construct

See how the image is the result of overlapping many circles to create the final drawing. Parts of the circles overlap with each other to form the desired figures.

Here is another example:

http://dribbble.com/shots/904051-Puffin

Do you know any good tutorial for learning this technique? I've been searching, but since I don't know what the technique is called, I've had no luck at all.