Reading and Interpreting Topographical Maps

Topographical Maps

• Topographical maps are large scale maps that show natural and cultural features of an area in detail.
• They are useful for geographers, planners, hikers, and the defence forces.
• To use a map, one must know how to read and interpret symbols, signs, and contour lines.

Contour Lines

• Contour lines are lines drawn on maps that join places having the same height above mean sea level.
• Each contour line is numbered and drawn at regular intervals.
• The number of the contour line indicates the height (in metres) of that area above sea level.
• The vertical distance, or the difference in elevation between two successive contour lines, is known as the vertical interval or contour interval.

Characteristics of Contour Lines

• The vertical interval remains constant for any given map.
• In the maps of the Survey of India, the vertical interval is always 20 metres.
• The horizontal distance between consecutive contour lines, called the horizontal equivalent, indicates the slope of the land.
• Closely spaced contour lines indicate steep slopes, while widely spaced lines represent gentle slopes.
• Uniformly spaced lines depict uniform slopes.
• When the lines are very far apart, it means that the land is flat.

Identifying Landforms through Contour Patterns

• Highlands with a steep slope on one side and a gentle slope on the other are called escarpments.
• Escarpments have closely spaced contour lines on the steeper side and widely spaced lines on the gently sloping side.
• Hills or mountains are shown by contour lines arranged in the form of concentric circles.
• Peaks of hills and mountains are indicated with the help of spot heights.
• Plateaus are broad highlands that rise abruptly from the surrounding land and have level, almost flat, tops.
• Plateaus are shown by evenly spaced contour lines surrounding an area with no lines or hardly any lines.
• Ridges are long, narrow, continuous areas of highland, consisting of a series of mountain peaks or hills.
• Ridges have long narrow and elliptical contours with steep slopes on both sides.
• Cliffs are very steep, almost vertical, rock faces and are indicated by contour lines that are very close together and sometimes merge to form a single line.
• Spurs are pieces of hard rock that protrude into river valleys and form an interlocking pattern with the contour lines.