Public display networks are increasingly seeking to provide personalised content to viewers. A key challenge in this area is to how to support conflicting personalisation requirements from multiple concurrent viewers. In this paper we present a four dimensional design space that describes a wide range of approaches to addressing this issue. This design space can be used by developers and researchers to understand how systems can be engineered to deliver an increase in the effective communications bandwidth to viewers while meeting their conflicting content requirements. This is the first attempt at systematically examining the challenges and design choices in this important emerging area.