Guzman’s Labelling Technique
1. Classify each vertex into one of the categories: ell, arrow, fork, tee, or other.
2. At each vertex, mark each incoming edge according to the role it plays at the vertex (e.g., shank of an arrow, stem of a tee).
3. Create single links between neighboring regions each time:
a. they are divided by a line segment at a fork,
b. they are divided by the shank of an arrow,
c. they are in corresponding positions of a configuration of two opposing tees with colinear stems.
4. Create a “node” for each region. Whenever two regions are doubly linked, connect their nodes with a “same object” link.