Identifying and interpreting relief
Relief is a central component of topographical and physical maps. Modern technology has enabled relief to be calculated to an even greater degree of accuracy. It is important for students to be able to identify and interpret relief on a map. This chapter explains the different types of methods used to represent relief on maps.
What is relief?
Relief is the difference in elevation (or height) between parts of the Earth's surface. The height of the land, in conjunction with information about the slope and shape, is very useful for many people, including surveyors, geologists, real estate developers and bushwalkers. There are a number of techniques which have been developed over time to accurately represent relief features on a map.
Early cartographers attempted to show surface features on maps by using the technique of hachuring. Hachures use short lines of varying thickness to 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. While hachuring was initially innovative for its time, it gradually began to be replaced since the actual height of the land was not depicted.
See image 1
Hill shading and spot heights
In the early 18th century, hachuring was replaced with a scientific form of hill shading and spot heights. Hill shading resembles a light and shadow effect. Valleys and the sides of mountains appear as though they are cast in shadow. This is a visually striking method, which is ideal for providing an overall view of the relief of an area. Hill shading, however, does not show height which means that it is no more accurate than hachuring.
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. While spot heights provide accuracy in elevation, they do not provide much information about the shape of the land. This is why they are often used in conjunction with hill shading, layer tinting and contour lines.
Layer tinting (colouring)
While spot heights show the height of the land, they only do so at certain points. To provide an overall image which conveyed height, a technique called layer tinting was developed. 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.
Layer tinting is most commonly found on physical maps. While layer tinting is useful, it does not show the detailed shape of the land.
See image 2
Contour lines are lines which connect points (spot heights) that are the same height above sea level. Most commonly found on topographic maps, contour lines are particularly useful, since they accurately depict the height, shape and slope of a landscape. The numbers which are featured on each line represent the exact height of the land at points along that line. The patterns created by the lines show the shape of the land. As a person becomes more familiar with the patterns, he or she is able to immediately identify different types of landforms. A pattern which resembles two circles with a space between them, for example, can be recognised as being two hills and a saddle (a dip between two areas of higher land). The slope can also be identified using contour lines. The closer the contour lines, the steeper the slope is.
A contour interval 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.
See image 3