Location-based information systems allow the user to access information in relation to the user's position in geographical space. This paper outlines navigational and social aspects of such systems. It is argued that location-based systems must allow users to participate as content providers in order to achieve a social and dynamic information space. Moreover, as these systems allow commercial and private users to annotate space with information on a mass-scale, information filtering techniques will become essential in order to prevent information overload and user disturbance. We present a number of content-based and social filtering techniques to support this. We discuss implications for implementation and we describe a system (GeoNotes), which takes some of these aspects into account.