A Simple Method to Quantify Bedrock Map Error

Geologic maps are foundational to geology. However, most geologic map contacts lack quantitative estimates of uncertainty, typically displaying known contacts as a solid line and uncertain contacts as a dashed line. To address this gap, an easily applied method is presented that provides a quantitative measure of the location of a mapped contact. This was done by creating a raster of the contact between two bedrock units and another raster of the bedrock surface. The mapped contact is where these two rasters intersect, or where their difference is zero. The error distribution of each raster was determined by using training and testing data. This allowed calculation of the overall error distribution of the difference of the rasters and the probability of the presence or absence of the upper bedrock unit. The probability of encountering either unit can then be mapped, with the contact located at the 50% probability contour.