Each contour line is composed of points which are all the same elevation. A contour interval is the vertical distance separating successive contour lines. Contour intervals vary on different maps, depending on the ruggedness of the terrain. Often a large interval is chosen in areas of steep slopes and a small interval is used in comparatively level areas. Contour lines generally are not angular, due to the forces of nature such as weathering and erosion that tend to round surficial features.
Every contour line closes on itself, either within or beyond the limits of the map.
Hatchured contours denote depressions. The elevation of a depression contour is the same as that of the adjacent lower contour, unless otherwise marked. There is a circular hill on the western half of the island and its summit is 140 feet high. This hill is very steep on its northern side and very gentle on its southern side. The highest elevation on the eastern half of the island is 60 feet.