Shaded relief maps show features on the surface, such as mountains, valleys, plateaus and canyons. Areas that are flat or have few features are smooth on the map, while areas with mountains and steep slopes appear more detailed and textured. Hill shading is done to simulate what the landscape would look like if the sun were in a particular position. The areas where the sun would be shining show brighter and the areas away from the sun would be darker. The resulting light-dark pattern causes the 3D illusion. Maps can also use colors to show variations in elevation.