Any land or elevations with contours illustrate the ‘undulations’ or surface variations of the site or area in question. These contours are typically displayed at quarter or half-metre intervals and are related to the site’s own grid system or the Ordnance Survey Grid System and height datum for accuracy. On elevations, these contours can reveal irregularities such as ‘sags or bulges’ in a structure, with details shown at 5–10mm intervals to capture even the smallest deviations.

The data, whether supplied by CD Surveys or a third party, is carefully processed and can be presented as a fully edited, three-dimensional Digital Terrain Model (DTM), offering a comprehensive and detailed visual representation of the terrain for in-depth analysis and project planning.