These kinds of contours are called supplementary contours or form lines. However, in some certain areas on a map, the normal contour interval is sometimes too large to represent a significant change in elevation, such as on level terrain, and thus, additional half-interval contours are added. The bold labeled contours lines are the index contours whereas the finer and un-labelled contours are the intermediate contours. Notice how only some of the contour lines are labelled with their elevations above mean sea level, while the others are not. This figure shows how contours are shown on maps. There are normally four intermediate contour lines between any two successive index contour lines. The Intermediate contour lines are finer than index contours and do not have their elevations labelled on them. These usually fall in between the index contour lines. The remaining contours are called intermediate contours. These bolded and labeled contour lines are usually referred to as the index contour lines. Thus, in order to make the map easier to read and less cumbersome, every fifth (5th) contour line from the mean sea level is usually labelled with its elevation and sometimes bolded a little bit heavier than the rest. Sometimes a map may have several contour lines such that it becomes difficult for the cartographer to label the elevations of each contour line. The Index, intermediate and supplementary contours. This figure shows how information regarding contour intervals is shown on the map, as taken from one of the US Army’s topographic map series 2201 (Dar Es Salaam 1:2,000,000 topographic maps) When supplementary contours are used, their interval is also indicated on the map. Information regarding the contour interval used in the map is usually shown in the marginal information on that given map. In other words, contour interval is the difference in height between any two successive contours on map. ![]() This vertical spacing between the contour lines is what is known as contour interval or vertical interval. These lines are drawn in such a way that they have to be evenly spaced vertically. However, for simplification, only the lines for certain elevations are drawn on the map. This figure shows how contour lines are shown on mapĬontour lines can be drawn for relatively any elevation. Contour lines lie perpendicular to streams and rivers.Usually, closely spaced contour lines indicate a steep slope while contour lines far apart indicate gentle slope. The spacing or gap between the contour lines represents the degree of slope.However, the only exception for this is ‘overhanging cliffs’ where many contour lines merge to form one contour line. This is because it is impossible to have a point on earth’s surface that can be at two or more different elevations above sea level at the same time. Contour lines never cross or intersect each other.Usually these numbers represent the exact elevation of land above sea level for all points along that line. ![]() ![]() ![]() They are numbered in either feet or meters, above sea level.They connect points of equal elevations above mean sea level.Generally, the contour lines have the following characteristics: Contouring is the most common method of showing relief on topographic maps because it has the ability to show all five (5) aspects of relief (shape, orientation, size, elevation and slope) on the map. The act of using contour lines in order to represent the relief of an area on the map is known as contouring. Contour lines are the lines drawn on the map connecting all points on the earth’s surface with equal elevations above a fixed datum line (usually the mean sea level).
0 Comments
Leave a Reply. |