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Solid Earth An interactive open-access journal of the European Geosciences Union
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Volume 6, issue 2
Solid Earth, 6, 727-745, 2015
https://doi.org/10.5194/se-6-727-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Solid Earth, 6, 727-745, 2015
https://doi.org/10.5194/se-6-727-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Method article 17 Jun 2015

Method article | 17 Jun 2015

Uncertainty in mapped geological boundaries held by a national geological survey:eliciting the geologists' tacit error model

R. M. Lark, R. S. Lawley, A. J. M. Barron, D. T. Aldiss, K. Ambrose, A. H. Cooper, J. R. Lee, and C. N. Waters R. M. Lark et al.
  • British Geological Survey, Keyworth, Nottingham, UK

Abstract. It is generally accepted that geological line work, such as mapped boundaries, are uncertain for various reasons. It is difficult to quantify this uncertainty directly, because the investigation of error in a boundary at a single location may be costly and time consuming, and many such observations are needed to estimate an uncertainty model with confidence. However, it is recognized across many disciplines that experts generally have a tacit model of the uncertainty of information that they produce (interpretations, diagnoses, etc.) and formal methods exist to extract this model in usable form by elicitation. In this paper we report a trial in which uncertainty models for geological boundaries mapped by geologists of the British Geological Survey (BGS) in six geological scenarios were elicited from a group of five experienced BGS geologists. In five cases a consensus distribution was obtained, which reflected both the initial individually elicited distribution and a structured process of group discussion in which individuals revised their opinions. In a sixth case a consensus was not reached. This concerned a boundary between superficial deposits where the geometry of the contact is hard to visualize. The trial showed that the geologists' tacit model of uncertainty in mapped boundaries reflects factors in addition to the cartographic error usually treated by buffering line work or in written guidance on its application. It suggests that further application of elicitation, to scenarios at an appropriate level of generalization, could be useful to provide working error models for the application and interpretation of line work.

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Boundaries on geological maps are drawn by geologists interpreting evidence (boreholes, surface features, etc.) in light of their geological knowledge. Boundaries are therefore uncertain, and this must be quantified so that map users can make sound decisions. In this paper we show how we can find statistical models of the uncertainty of boundary positions by a structured method to elicit the tacit model of uncertainty which experienced field geologists use when interpreting geological maps.
Boundaries on geological maps are drawn by geologists interpreting evidence (boreholes, surface...
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