This report reviewed a number of measures of complexity associated with visual displays and analyzed the potential to apply these methods to assess the complexity of air traffic control (ATC) displays. Through the literature review, we identified three basic complexity factors: numeric size, variety, and rules. Essentially, all the complexity measures could be described by these factors. Through the analysis of available complexity measures, we showed that neither information complexity that focused on the system nor cognitive complexity that aimed at observers could provide a complete description for ATC application.