What constitutes an effective representation?

This paper presents a taxonomy of 19 cognitive criteria for judging what constitutes effective representational systems, particularly for knowledge rich topics. Two classes of cognitive criteria are discussed. The first concerns access to concepts by reading and making inferences from external representations. The second class addresses the generation and manipulation of external representations to fulfill reasoning or problem solving goals. Suggestions for the use of the classification are made. Examples of conventional representations and Law Encoding Diagrams for the conceptual challenging topic of particle collisions are provided throughout.