Everything is relative. Even your location is! Normally we express location in terms of the most nearby city or street, or in terms of latitude and longitude, which is relative to the center of the globe. For automatic location determination, a GPS device can be used to calculate latitude and longitude based on received satellite signals. Less accurate, but more easy because almost everyone has his own mobile phone, is it to determine location based on the nearby GSM antennas.
The problem is that each antenna only discloses a cell ID but not its location. Some telecom operators offer a positioning service for their subscribers, but normally this is an expensive service, operator dependent, and not free of privacy issues. Therefore we propose an approach of mapping the GSM landscape, by driving around with a GPS-enhanced phone that updates the (latitude,longitude,cell ID) tuples on a central server. The advantage is of course independence of operator, easy roaming over country borders, and low costs. But the disadvantage is limited coverage in the beginning.
The cell ID database now contains more than 10.000 cells in 14 (mostly European) countries. It estimates the location of GSM cells based on all measurements of people that have traversed through that cell. This location information can be used to supply people with an estimate of their location based on cell ID only, so without GPS or operator who charges several eurocents per request. The location information can be used to trigger different location-based services, including the new home finder, the friend finder, easy meeting point, et cetera. The cell ID database offers a web service to store and request cell information programmatically.
The database contents are also visualised in SVG. There are maps on country, region and cell level. The measurement points indicate signal strength: red is low, green is high. By clicking on a cell in the country or region map, you are redirected to the cell map. And by clicking the country or region keywords on the right of the cell map, you are redirected to the country or region map. An example of a region map for Amsterdam is shown below.
The data is collected by volunteers and available free of charge (for non-commercial purposes).