Relief and 13 Ways of Representing And Identifying Relief on a Map

On our topic about relief, We shall now explore the different ways of representing and/or identifying relief on a geographical map.

•Relief is the difference in elevation (or height) between parts of the Earth’s surface
•Relief is a central component of topographical and physical maps
•There are a number of techniques which have been developed over time to accurately represent relief features on a map.

Ways of representing/Identifying and interpreting relief

Hachuring

•Hachures are short lines of varying thickness which show the shape and slope of the land.
•In accordance with this technique, the steeper the slope is, the thicker the lines are which represent it.
•They do not represent exact elevations, but are mainly used to show large, rocky outcrop areas.
• Hachures are used extensively on small-scale maps to show mountain ranges, plateaus, and mountain peaks.

Hill shading

•This method also shows the steepness of slope but it differs from hachuring in that it does not show the steepness using lines but uses shadow .
•This method does not show the exact height of the slope

spot heights

• Spot heights are used to show the exact height of the land at a particular point.
• Spot heights are depicted using a dot (or triangle) and a corresponding number, which represents the altitude (height above sea level) at that point

Layer tinting (coloring)

•Layer tinting uses different colours (or shades) to represent different heights.
•It is a mapping convention for darker colours to signify greater height.
•When using layer tinting, green is often used for low land, yellow for higher land and brown for the highest land.

Valley

•This is along depression usually occupied by a river.
•On contour maps, valleys are shown by a series of V-shaped contours pointing upstream

Ridge or Mountain range

•Mountain usually occurs together in mountain ranges with some peaks higher than others.
•A ridge is a long narrow area of highland sometimes almost flat on top.
•The contour lines of range or a ridge may be drawn close to another, indicating the presence of steep slope

Spur

•This is a highland which extends towards longer ground.
•On contour maps, a spur is shown by V-shaped contour lines pointing towards lower ground.

Watershed

•Watershed is an area of high ground that separates the headwater streams of two river systems.
•Mountains, ridges and spurs can form watersheds.
•Water flows down opposite slopes into different rivers

Gorge

•It is a narrow, steep-sided river valley.
•Gorges have very narrow floors and valley walls that are almost vertical.
•On contour maps, gorges are shown by contour lines that drawn close together and that approach very near to the river from both sides

Gap

•It is an opening or way by which a natural mountain barrier can be crossed.
•If there is a permanent road or way through a gap then it is called a pass.
•The road between Livingstone and Lusaka goes through a gap in the Munali hills.

Col

•It is a depression between peaks along ridge.
•While its shape is similar to a gap, it is usually still too high in the mountains to allow a permanent route to pass from one side to the other.
•The shape of a col resembles someone’s neck when they are lying down.

Saddle

•It is so called because it resembles a saddle of a horse.
•The saddle includes the peaks on each side as well as the depression between them,so it is wider than a col.

Contour Lines.

•Contour lines are the most common method of showing relief and elevation on a standard topographic map.
•A contour line represents an imaginary line on the ground, above or below sea level.
•All points on the contour line are at the same elevation.
•The elevation represented by contour lines is the vertical distance above or below sea level.

• A contour interval (VI) is the difference in height between contour lines.
•Contour lines always increase or decrease by the same amount.
•This means that if one contour line represents points 50 metres above sea level and the next contour line shows points at 100 metres above sea level, then the third contour line will be 150 metres above sea level. In this example, the contour interval is 50 metres.
•The Horizontal equivalent (HE) is the distance between two contours expressed as a horizontal measurement.
•The horizontal equivalence will vary according to how the steep or gentle the slope of the land is.

Trigonometrical points

These are found at the hill summit on which the height of the hill is shown. Calculating distance

Measuring straight line distance:

The following steps are followed:

a. Draw a straight line connecting the two points as shown below in the example.
b. Get a piece of paper and place the edge of the piece of paper along the line and mark the two points on the piece of paper.
c. Measure the length on the linear scale by placing the piece of paper along the scale with the first marked point at 0.

Measuring distance not straight (i.e. Road, Railway) or River:

What is the distance of the road from grid square 8144 up to the bridge in grid square
8749.

•This can be done in the following way as follows:

A. Using a string

•A string is put along the road starting at easting 81up to northing 50.
•The string is then straightened and put along the scale and measure the distance it represents.

Measuring Bearings

•Bearing is an accurate way of giving the direction of one place in relation to another
•Bearing is the direction measured as an angle.
•Bearing is measured in degrees.
•The measuring of the angle is made from the true north and measured in a clock wise direction.
•True North is shown by the vertical straight line.
•True North is known as Geographic North or Map North.
•Magnetic North is shown by the arrow pointing to the west of True North.

1.What is the bearing of B from A= 66°
2.What is the bearing of D from C= 180° +50°= 230°

Gradient

•Gradient is the steepness of a slope.
•To calculate the average gradient, there is need to know:

♦♦♦ The altitude or height of two points.
♦♦♦ The distance between the two points

Then find the different in height between two points

Then measure and convert the distance in height of two points by their distance apart.
Finally divide the difference in height of two points by their distance apart (horizontal equivalence)
Therefore gradient is calculated by the following formula Gradient = Difference in Height

Difference in equivalence

Example:

•Find the average gradient between point A, 3000 metres high and point B, 2,000. B is 10km from A.

❖Difference in height between A and B is 3000-2000=1000 meters
❖The distance between A and B is 10 km (10km x 1000 m) = 10,000 meters.
❖Divide 1000 by 10000 as shown below:

Gradient = 1000 /10,000
= 1 or 1 in 10