Linear features (shown as polylines) in BGS Geology 50k are used to portray geological features and concepts that are normally depicted on maps in linear form, rather than polygonal form. The data is presented at 1:50 000 scale. Onshore coverage is provided for England, Scotland, Wales and the Isle of Man. Approximately 99% coverage is available and BGS is committed to completing the coverage, and ongoing updates as part of its ongoing national survey. Linear features are associated most closely with the bedrock theme either as an intrinsic part of it for example marine bands or affecting it in the case of faults. However, landform elements are associated with both bedrock and superficial deposits. The linear features are organised into seven main categories: Alteration areas: areas indicating zones of change to the pre-existing rocks due to the application of heat and pressure that can occur round structural features such as faults and dykes. The linear feature defines the estimated boundary of the change. Fault: where a body of bedrock has been fractured and displaced by a large-scale process affecting the earth’s crust. The linear feature is used to represent a 3-dimensional plane of disruption on a 2-dimensional map. The line itself typically defines a broader zone of displacement/failure, rather than an individual fault plane. Fold Axis: where strata are bent or deformed resulting from changes or movement of the earth’s surface creating heat and pressure to reshape and transform the original horizontal strata. Folds appear on all scales, in all rock types and from a variety of causes. The linear feature is used to represent the “hinge” of the folds (which is a 3-dimensional plane being represented on a 2-dimensional map). Fossil horizon: where prolific fossil assemblages occur and can be used to help establish the order in which deposits were laid down (stratigraphy). These horizons allow correlation where sediments of the same age look completely different due to variations in depositional environment. The linear feature is used to represent a layer of material that is typically too thin to be shown as a polygon on the map. Landforms: define the landscape by its surface form; these include glacial features such as drumlins, eskers, and ice margins. The linear feature is typically used to represent a boundary, or centre line that defines the form of the feature. Mineral vein: where concentrations of crystallised mineral occur within a rock, they are closely associated with faulting but may occur independently. The linear feature defines the estimated extent of the mineralised vein, but does not indicate the volume of wall rock that has been affected. Rock: lines representing beds of notable geological materials and key marker beds, e.g., coal, gypsum, ironstone relevant to the Bedrock theme. The linear feature is used to represent a layer of material that is typically too thin to be shown as a polygon on the map. The data are available in vector format (containing the geometry of each feature linked to a database record describing their attributes) as ESRI shapefiles and are available under BGS data licence.
