The British Geological Survey (BGS) has embarked on a program of digitization of its survey-scale maps. Objectives include linking the digital map data with existing relational database tables containing spatial information, structuring composite spatial and aspatial queries against these linked data sets to produce a wide range of derivative maps, and improving the cartographic quality of the standard geological maps. The geological map is transformed into a geological spatial database, and requires implementation within Geographic Information Systems (GIS) software. The first step in implementation was the construction of a logical model of the geological information shown on the map. The entities identified in the logical model were implemented either entirely within the relational database, entirely within the cartographic file structure, or as full GIS features comprising graphic elements linked to a relational database table of attributes. Graphic elements were digitized within a CAD environment using a graphic data structure that allowed both subsequent loading to the GIS feature structure, and the automatic population of frequently occurring attribute values. Standard and derivative geological maps are produced using software which enables sophisticated output cartography to be attached to graphic elements according to their database attributes. This process separates the cartography used when digitizing the data from that of an output map. Copyright (C) 1996 NERC.
