Cryptography is the study of coded messages, or "cyphers." Coded messages have been used for thousands of years to convey hidden meaning to those who know how to find it. Shapes, numbers, colors, lines, sounds and smells are all used to code messages. More complex forms of cyphers require complex algorithms to both code and decode messages. Basic cyphers use simple substitution to replace shapes or symbols with letters or words.
A diagrammatic cypher utilizes shapes to represent letters, words, concepts and ideas. Diagrammatic cyphers used in schools teach rudimentary cypher decoding. Deciphering diagrammatic cyphers requires simple substitution of diagrams, shapes or lines to deduce messages.
Shapes have been used as symbols for many thousands of years. Simple symbols adorn cave walls of prehistoric times. More complex symbols, such as hieroglyphs, represent words and ideas. Many of the letters in modern alphabets are complete polygons, such as the letter "O," while many letters use lines in specific shapes to convey meaning.
The Polygonian Alphabet, a diagrammatic cypher, is used by the Voyager Learning program to teach about cryptography and introduce writing in symbols. The learning activity provides a set of polygons corresponding to specific letters of the English alphabet. The activity requires deciphering the hidden message by replacing polygons with corresponding letters of the alphabet.