Social network services have become one of the most important means of communication, information exchange and entertainment on the Internet. They enable users to create personal profiles, to manage contact lists and address books, to communicate with other members, to receive and to send messages as well as to share media. In the course of this thesis, the social network I go... is designed and implemented. In contrast to traditional social networks, I go... offers services with a geographic-coordinative background. These services comprise, amongst others, the following functions: The user can mark his place of domicile in a map and obtains a notification as soon as any of his friends turns up near him.The user can post all of his future activities to the network, mark their locations in a map and show them to all of his friends. Moreover, I go... can access the GPS receiver of the user's mobile device and, thus, determine his current position.The user can offer rides to other members or search for existing rides in the network. Rides are stored and calculated in a coordinative wayAs I go.... runs as an application on Facebook, users are able to log into the network with the help of their Facebook accounts.The thesis is divided into two major parts: the first part discusses the practical implementation of the web service as described above. The functions and services provided in I go... as well as the technologies used for its implementation are described in detail. The second part provides the reader with an overview on the technologies, the methods and the fields of science that can be regarded as the web services' theoretical framework. I go... operates on the interface between a social network, online visualization of geoinformation, routing in a network, a location-based service and a database management system.