Follow the yellow brick road: Lessons from the path to seamless digital geological map data from Oz(tralia)
|Location||International Geological Congress,oslo 2008|
|Author||Bibby, Linda M.; Callaway, Graham A.; Higgins, Dave V.; Morand, Vincent J.; Simons, Bruce A.; VandenBerg, Fons|
|Holding Date||11 October 2008|
GeoScience Victoria adopted a new approach to its mapping and compilation activities in 2006 in an attempt to distil more than 150 years of unfettered geological investigations into a coherent geological map dataset. Our aim is to produce an internally consistent compilation of existing geological map information, supplemented and enhanced by new mapping in critical areas. Although we have been making digital geological maps since the mid-1990s, some of which have been at State-wide scales, this is our first attempt to produce seamless datasets at all scales. But how do you merge maps of different vintage, quality and purpose?
We assess individual maps against modern geophysical data (gravity, magnetics and radiometrics) and recent aerial photography, supported by corporate databases that provide both direct and indirect evidence of the geology (including topography, site observations, boreholes and mines). Other sources of data include our oldest maps (dating back to the mid-nineteenth century), which capture excellent observational data as face notes, and 1940s parish plans that show locations of thin sections, many of which are still accessible in our collections. Targeted field checking is used to verify the compilations.
Rationalising the wide range of unit symbols on previous maps to provide a consistent geological framework posed problems not present in traditional map-making. Our attempts to resolve the tangled nomenclature of a large flood basalt province prompted vigorous debate at a national level, and stressed the importance of engaging the broader geoscience community. Another decision, that it was geologically acceptable for subdivided units to merge with their undifferentiated counterparts across former map borders, helped achieve our project deadlines, but one junction between four original maps has Group-level data in opposite corners and formation-level units in the others, creating a very un-seamless area right in the middle of the map data!
The new data layers include surface geological units, their boundaries, and major faults. This small subset of the vast amount of information crammed onto a typical geological map is still a large investment for a relatively small organisation. The move away from well-established work processes with a clear set of products forces business-driven decisions of what to collect—and, more importantly, what to leave out—and involves some very un-geological activities such as ‘stakeholder analysis’.
We have found that the move from traditional map-making to database building is very challenging, and will remain so for some time yet. However, the benefits of the new data for us and our clients provide compelling reasons for us to continue.