Lindenbeck, Ch., Ulmer, H. & Schulz, M. (2007): Open Source technology in WebGIS application development: implementation of a borehole information system. Abstract The application of web mapping technology is discussed using the example of a borehole information system called "Bohrdaten Portal" (BDP) of the city of Hamburg. Two extensive Open Source projects have been integrated to build this complex WebGIS system. Three years of operation of BDP have shown that the reliability and stability of complex heterogeneous Open Source applications have been widely underestimated in the past. The BDP is designed as a specific information system with a restricted access in the intranet of the city of Hamburg. The modular architecture helps to integrate the functionality of graphic representation of borehole data within the geoinfrastructure of the so called "Metropolregion Hamburg". Modules of the BDP are also used as an extension of the GIS workstations (ArcGIS) in the city administration.