Location is the most obvious and easily exploitable piece of information upon which context-aware applications can rely. Based upon the narrowly-defined requirements of specialised location-based services, a number of programmatic interfaces, text-based or binary formats and protocols have been proposed to handle it in a more or less ad hoc and piecemeal fashion , most of them failing to capture the more general theoretical framework in which the location problem could be set.
The grand idea behind using physical location to address information is to bridge the gap between the informational and physical worlds , which prevailing desktopcentric interface metaphors have contributed to widen. This goes much beyond the cellular-network-location-based services already on offer, and even beyond the more general context-awareness idea. Such a far-reaching vision of "information in places", "worldboard", "situated information spaces", has been eloquently articulated , and partially illustrated in such projects as MapPlanet  and Confluence. In this view, the physical world is the most compelling interface metaphor to cyberspace , and geo-location is used, not only as the user 's own position, but as a unifying navigation anchor and an intuitive representational tool, to make sense of the overwhelming multidimensionality of the information space.
As such, location information may be used in either an abstract or concrete sense, from the smallest to the largest possible scale. What is located may be either the user himself, the information he retrieves, the physical objects or the other people with whom he interacts .
This paper attempts to give a broad outline of a location architecture that could encompass the diverse requirements of all these potential applications. We begin by specifying the requirements for a location infrastructure with different models of physical space corresponding to increasing levels of abstraction. From this we try to describe a general template for a location infrastructure that draws upon an analogy to the layered models of network protocols and examine one first example of a minimal implementation based on Jini .
 Work partially funded under the ITEA Ambience Project.