After reviewing lots of interfaces that enable location-awareness in both physical and virtual world, I discriminated criteria to describe them. There is no real formal classification of the MLA tools diversity. Nevertheless, according to Jones et al. (2004) in their conceptual framework of location-based and social applications, three characteristics are prominent: the focus of the service (people or place), the content of the awareness (absolute location, relative location or proximity), the time-span (present versus past, which has been referred to as synchronous versus asynchronous).

These characteristics offer a starting point for developing our own classification of MLA tools. Based on Jones’ framework, I discriminated five criteria, as represented on the figure below.

The mode of capture of users’ location, which can be self-disclosed (user initiative) or automatically grasped with different degrees of accuracy. For example the user can be asked to send his or her own location so that it can be displayed on the contacts’ lists.
The type of information that is stored by the system that falls in two aspects: the position and the referential. Position could either be discrete such as place names or continuous with coordinates in a 2D or 3D space. This corresponds to the space/place distinction we discussed earlier. Of course, there is a need to have a referential, which can be the physical environment, a virtual world or a shared document.
The mode of retrieval: user can access information about others’ location in space upon request or by receiving it automatically (if the application is opened). If the retrieval is based on the user’s intiative, it can be based on two focuses: the user can look for information about people (“Display my friends location”) or look who is located in a specific place (“Who is in that room”). This is what Jones et al. (2004) described as a people or place focus.
The scope of retrieval: whether it is geographic (representation of the proximity or the whole space), social (displaying everyone or only specific contacts such as friends) or bound to a specific period of time. This last characteristic corresponds to the different between synchronous (information about real-time position in space) and asynchronous MLA (information about real-time and post position in space).
The format of delivery that can be described with two sub-characteristics. On one hand, the location referential can be absolute (a place or location coordinates) or relative (indication that a friend is close to you for instance). On the other hand, the final format of display could be verbal (name of a place), symbolic (shown as a symbol), or geographic (depicted on a map metaphor).

Any comment/criticism on that is welcome.