GeoLegend: A database system for managing geological map units in a geographic information system

Abstract

Geological map units commonly have labels and legends that are incompatible between neighbouring maps. GeoLegend is a relational database structure for use with Geographic Information Systems (GIS) that allows map units to be reclassified consistently from map to map and automatically compiles unit labels and legends. It is presently being used to generate customised geological maps within a 33 000 km 2 area of Newfoundland, Canada. The system uses a single set of linework, digitized from bedrock geology maps at the most detailed scales available. For each area, the most reliable map is chosen, and the digitized maps are then joined together to form a continuous mosaic of regional extent. No changes are made to the linework as originally published, so some mismatches remain at map boundaries, but the most serious inconsistencies are eliminated by rationalising the classification of units. A map can be generated for any part of the continuous coverage, irrespective of original geological or topographic map boundaries. Each polygon within the map mosaic has a unique identifier which links it to GeoLegend and allows the retrieval of geological data pertaining to that polygon. GeoLegend organizes these data so that they can be used to control the level of detail shown on a map. Detail can be changed both between and within maps to suit a variety of scales and uses. GeoLegend produces a consistent set of unit labels, a legend and a list of references to source maps and legend descriptions; all of these are specific to whatever part of the map mosaic is selected and reflect the levels of detail chosen for the map. Data files can be produced for use with GIS viewing software, allowing the creation of maps that can be searched interactively by unit, age, rock type and other geological criteria.