INCIDENTS along the boundary of the enclosure let the draughtsman know something structurally significant has occurred.
An INCIDENT is taking place that requires a determination from the draughtsman as to its cause.
These Incidents result from Intersections, Interlocks, Insertions, Intervals or a combination thereof. They need to be understood by the draftsman; they describe how the form units relate to each other, how they overlap (Intersections) how they articulate (Interlocks/Insertions.)
They also divide the enclosure into verticle and horizontal (Intervals) which is a valuable proportional tool.
INTERSECTIONS: Intersections occur when one body part overlaps another part to the body i.e. one leg overlaps another leg/. One needs to be aware of what is overlapping what and determine whether they are looking at a (Y) Intersection or a (T) Intersection i.e. is the overlap moving away (Y) or toward (T).
INTERLOCKS, INSERTIONS, AND PASSINGS: The upper and lower limbs are held together by mortise and tendon. They originate with ball and socket joints at the shoulder and hip and have hinge joints at the knee and elbow. The adjoining muscle groups are capable of moving these mechanisms in any manner that their construction permits.
As this movement occurs, the muscles expand, shorten and bulge, creating smaller wedge shaped forms which articulate with the larger masses. These muscle groups pass into, over and around one another. It is these parts passing into or over each other that gives the sense of interlocking. The form either passes around or enters into the outline of the visible boundary of a figure.
It should be an indication of what it is: the outline of a form. Within this outline, for the same reason, forms pass into and over other forms, they Interlock.
The drawn outline of the figure either gives no sense of the diverse smaller forms of which it is composed. Or, maybe so drawn as to give a sense of depth, i.e., the interlocking and passing of smaller forms within the larger masses to convey volume and solidity.
• INTERVALS: Horizontal and Vertical intervals off of center lines are a great help to the draughtsman. They not only position off the center line but also form a gird that isolates pieces of the external boundaries and the internal value patterns.