Information theoretic design of space-constrained touch-based user interfaces

In this paper we present a simple rule-of-thumb for creating space-constrained touch-based user interfaces (such as for a touchscreen mobile device). By looking at user interfaces as communication channels, we obtain the rule that the size of any UI element should be proportional to the square root of the probability of selection by an expert user. This relation is then used to obtain a metric for the clarity of a user interface by measuring the Interface Entropy of the system.