Relief can be represented in a two-dimensional map either through contour lines or through a raster format gridded array of elevations. Contour lines connect points of equal elevation. At regular intervals index contours are marked with elevations so a reader can more easily determine the elevation of surrounding locations. They are the preferred method for analogue topographic maps. The grid approach is used in digital mapping and known as a digital elevation model (DEM), where each raster cell represents an elevation. Scaling of the cell z value in relation to the x and y value results in terrain exaggeration, which aids visualization of topography.
DEMs are used for terrain analysis and can be used to obtain derivatives such as slope and aspect. DEMs are obtained by interpolating point elevation observations, which are historically retrieved from surveyed point data (e.g. GPS locations), but more recently from LiDAR and/or Structure from Motion point clouds. TIN (triangular irregular network) analysis is commonly used for point data interpolation, in order to derive a continuous elevation surface.