GEOLOGICAL MAPPING IN URBAN AREAS - THE BGS EXPERIENCE IN LONDON

The British Geological Survey has established the LOCUS (LOndon Comput erised Underground and Surface) geological project, whose aim is to pr ovide geological maps and interpreted data for London. The resultant h igh-quality model has already proved valuable in projects ranging from the site-specific to strategic overview. The perceived requirement fo r geological information in urban areas is to support land-use plannin g, environmental matters, project planning and civil engineering. With increasing demand for urban geoscience information, the Survey has de veloped a geologically attributed digital map-production system. This system is structured to provide, on demand, up-to-date colour-printed geological maps at any scale. Thematic maps illustrating specific aspe cts of geological data are produced also. The output is made available in hard-copy and digital form for GIS applications. Additionally, a d igital relational database has been established using information from 20,000 borehole records for London. Borehole site data and levels, th e base of man-made ground and three key geological horizons are used f or three-dimensional computer modelling. For London, these horizons ar e the base of the superficial deposits, which are essentially the sedi ments deposited by the River Thames; the base of the London Clay, whic h underlies much of London and is the best tunnelling medium; and the top of the Chalk, an important aquifer in the London Basin. Implementa tion of digital map production and the rationalisation of, principally , borehole information has enabled routine production of computer-gene rated geological models of London and provided the means to visualize automatically a range of information from point data to 3-D models.