ANCHORS AWEIGH - MAPPING ON THE EDGE OF REASON

The high regard in which geological maps are held gives the knowledge they portray a longevity beyond that reported through other means. Inheritance of past knowledge is fundamental to scientific advance – but only if recognised and acknowledged. Knowledge on maps consists of data (spatial distribution of rock-types and measurements) and interpretation (e.g. correlations between rock outcrops as formations, boundaries and other discontinuities). It is their ability to show interpretation, allied to spatial data, and the corollaries of geologic histories that give geological maps such value. Yet their status within our science, together with un-acknowledged interpretational content, means that existing maps can act as un-recognised anchors that bias subsequent interpretation. So they are inherently non-unique representations: Maps capture the geological knowledge and biases of the interpreter – at the time (or times) of interpretation. In regions of complex structure or of poor outcrop the issue can have serious consequences. The further challenge lies when new maps are compiled or modified from existing maps, because different information will be given different priority in these various versions.

Weakly acknowledged anchoring influences much digital mapping and visualisation: The starting point for re-evaluation of the structure of an area will commonly be a DEM draped with geo-rectified historical mapping. Thus old interpretations can be inherited uncritically, hindering the progress of new ideas. Project management protocols, such as those embedded in seismic interpretation applications, could reduce these risks and provide mechanisms for comparing multiple realisations. And metadata could assist charting the interpretational decisions associated with specific components of geological boundaries. Embedding such protocols will be critical for the future assessment of biases and uncertainties in models of subsurface geology and new geological maps.