The following are examples of NOTAN
Notan images (Source Google images)
The image clarifies what is NOTAN: bi-color, black and white, or better dark and light drawings.
The term come from Japan.
Basically, you draw in a very (but not quite so) simple way and in 2 dmensions: flat drawings, no idea of space and realism, that is.
NOTAN design in composition
If you want to have a look at a possible use of Notan in composition, here is a demonstration for an underpainting in Notan.
The example is taken fromt he nice emptyeasel.com tutorial. Have a look there!
It is also useful to remind you of the grey scale values and the value isolator (a mid-grey paper with a whole in the middle to compare tonal values. For more visual adds check my artist tools webpage here.
The scale of Grey ...with all relative relationships: what is shadow for one area is highlight for another area (check the middle grey bar in relation with the grey values)
Value Comparing tools. Cut out the white area and look through to see which value you see in plein-air painting or drawing.
You can also use a simple mid-grey square with a whole and look through.
How to use it: everything which is darker than the grey cardboard is black. That's it!
(if the grey area is the same grey color as the cardboard you can decide: either black or white) .