Relief features on land have varying elevations above sea level and varying degrees of slope. The elevation of selected points like hill summits or valley floors are indicated by spot heights, which are given in feet or metre above sea level. When the heights of many points are known in an area, contour lines are drawn by interpolation to join places having the same height. Contours or contour line are drawn as a result of detailed survey of an area. Hence contours are the most precise method of representation of relief features on maps. Contours are usually drawn at an interval. The interval between two successive contours is called the contour interval or vertical interval. This may be 20, 25 or 100 meters depending on the scale of the map.
When contour lines are close together, it indicates a Steep slope: Gentle slope is represented by contours, which are far apart. Convex slope is represented as gentle slope at higher levels and Steep slope at long levels. Concave slopes are indicated by Gentle slopes at long levels and Steep slopes at higher levels. Uniform slope is indicated by uniform spacing of contours.
In large scale topographic maps contours are used to represent relief features.
Hill shading. Sometimes hill shading is combined with to give a visual impression of the map. It is generally assumed that a source of light is situated in the Northern corner and the Eastern and Southern slopes are shaded as though they are the shadows cast by the relief features. Hill shading is used on topographic maps published by survey of India.
Hachures are drawn in areas where precise surveying has been done. In the early days Hachures were more widely used as many areas were not surveyed accurately. Hachures are short lines drawn in the direction of slope of the land. Gentle slopes are indicated by thin lines: Steep slopes are shown by thick lines drawn close together. Level land such as hill tops and valley floors are left blank. Hachures give a good idea of configuration of the land. They do not give any indication of height of the land. Hachures are not now commonly used because they occupy more space in areas of Steep slopes and no other information can be shown.
Types of Slopes.
(1) steep slope
(2) gentle slope
(3) uniform slope
(4) concave slope
(5) convex slope
Layer coloring method is adopted to represent relief features on atlas maps and wall maps. Only a few selected contours are drawn at varying intervals and the space between the contours is shaded in colors. Low lands are shaded in dark green. As the land rises in elevation, higher elevations are shown progressively in shades of light green, light brown, dark brown, crimson and red. Snow-capped areas of mountains and Polar regions are left white and not shaded. A key is given to indicate the altitudinal range between each colour. Colors are shaded lightly so that other natural and cultural features and names can be printed on the map.
"The world is a book, and those who do not travel read only a page", St. Augustine said. Here at www.travel-university.org we believe that every page must be read and explored. Travel is an avenue of learning that no text or classroom can teach. The world is a living classroom and you the student. We invite you to the www.travel-university.org library where you can read general interest and detail oriented articles.
