This paper examines the implementation of a notification- and visualization-system generally aiming to
provide users with a comprehensive possibility to spontaneously get in touch and stay in contact with their
friends and acquaintances. Essential part of the system is the mobile application, based on the Google
Android platform, which can be used to keep track about the spatial positions of a user's contacts. One of
the main aspects of the presented system is the automatic contact alert mechanism, which notifies users
every time that one or more of their contacts are located nearby. In case a contact is in vicinity the
application initiates a visual and/or acoustic signal on the mobile device.
At any time users are able to easily take a glance at a geographical map displaying the surrounding area of
their current position and all of their online contacts within this area. Moreover, users have the possibility
to retrieve further information for each of their displayed contacts (if provided by the contact), such as their
current activity or specific location metadata, e.g. the speed, direction and distance of a contact to the user's
own location. Additionally, a user can explicitly look out for a specific contact, regardless of where the
contact is located globally, as long as the contact is logged on to the system and shares his/her location
information. Furthermore, the system supports the exchange of location- and event-messages, enabling
users to easily share location data or set up appointments with their contacts.
Another main feature of the prototype is the automatic location context determination, which provides users
not just the raw location information on a map, but also the contextual meaning specified by the contact.
That means users can see that a contact is e.g. at home or at work, when the user is indeed within the spatial
range of his home or work location. The system can detect automatically if a user reaches one of his most
common places and provide this information to contacts (allowance required).