Shared Contour and Shared Edge, mean the same thing. Graphically speaking, it is when two shapes next to one another have the exact same outer edge for at least a portion of their overall outlines or outer edges. It is important to realize that these two shapes DO NOT overlap. They are simply right next to one another.

When the line that describes each of these adjacent shapes goes completely around each of them then we can say those lines are explicit lines. When at least a portion, or all, of the line/edge that is shared by both of those same two adjacent shapes is purposefully missing or not there, we say that the edge is implied. That missing line is called an implied line.

Sometimes that “missing” or implied line can be used to graphically indicate strong or intense lighting effects and give three-dimensionality to a shape.

The use of implied line is an essential element in the specific Gestalt principle of Figure and Ground Reversal. As such the creative use of it can have a very strong and dynamic affect on visual perception.

In the example above, the designer has taken creative liberty with the shared contour edge’s shape or direction—giving slight preference to one of the shapes (letters) while remaining similar (but not exactly the same) as the other’s contour. One of the letters then makes additional use of implied line to create a little visual trick of figure ground reversal.