Type 17 designs are made up of polyomino shapes. The term polyomino is a mathematical one of recent coinage ( coined by American mathematician Solomon W. Golomb, who has written a book on the subject). A polyomino is a two-dimensional shape formed of identical squares that attach themselves to each other corner-to-corner and end-to-end. The simplest example, a domino, a 1:2 rectangle, is known from the popular board game. A two dimensional domino, unlike the Dominoes playing piece, has no thickness. It is a polyomino contructed with two squares. A polyomino of three squares is a tromino or triomino, as it is also called. There are two possible tromino shapes: a 1:3 rectangle and an L shape. This L shape, the L tromino (sometimes also called the right tromino) is one of the commonest and most basic shapes of of the Type 17 designs. Other shapes made of more squares are the tetrominoes (made of four squares, with 5 possible shapes), the pentominoes (made of five squares and having 12 possible shapes). As more squares are added the possibilities increase geometrically. Not all the shapes are artistically interesting to me, and I tend to use many types of L shapes as they make more interesting designs.
Many Type 7 designs are solid, that is, they have no negative space. Some have negative space, usually with squares and rectangles forming the negative (or left-over) space. A few border designs consist of shapes that are surrounded by much space. Some consist of shapes that articulate with bands. In terms of the number of designs, this is my largest category, with over 2,600 designs. The Type 17 sub-family of the N.S.A.P Series, is discussed in the section for that group.