SIMPLIFYING THE PROCESS OF UPDATING AND INTEGRATING DIGITAL GEOLOGY

Digital mapping in the Earth sciences has long-used polygons to define map units. However, polygons are prone to errors in editing and edge matching if they are used to compile, update, and integrate digital geological maps. These errors cause discontinuities, slivers, gaps, and overlaps that are hard to fix. Using polygons as part of the base also makes it excessively time consuming to reconcile geometric differences among shared geological boundaries (e.g., fault contacts). To avoid these problems, the British Columbia Geological Survey has developed a ‘geologic framework data’ (GFD) model. We have dispensed with polygons in managing geological maps. Instead, our GFD model only consists of centroids (describing map units) and lines (defining geological boundaries) to edit, revise, and integrate maps. Bedrock polygons are not part of the GFD but are generated from GFD in the finished map. Adopting the GFD model allows us to develop ‘checking-out’ and ‘anchoring’ mechanisms to eliminate map boundary issues in edge matching when maps are integrated. Before a new mapping project commences, the ‘checking-out’ process extracts the GFD data for a given area across an extended regional context to include map units and boundaries in the project area without being clipped. The outermost boundaries of this extended project area are tagged as ‘anchor lines’, with nodes on the anchor lines as ‘hooks’ that connect to ‘rode lines’ in the project map. When mapping is completed, the updated GFD is returned to the GFD base, with rode lines in the project map snapped to the hooks in the GFD base in lieu of edge matching.The British Columbia Geological Survey implemented the GFD model in a PostgreSQL/PostGIS database, making it possible to handle large volumes of data, and permit multiple users to perform concurrent operations on the same GFD base. We have developed applications as part of the spatial database management system to automate checking-out, anchoring, and integration. These applications not only simplify the integration process, but also streamline rules-driven data quality checks, content standardization, change audits, map legend updates, and production of custom maps for delivery via web services.