Methods of Representing Relief of the Landscape on Topographic Maps

Relief of a landscape is basically the physical configuration or appearance of such a landscape taking into account the elevations, slopes, and shape of natural features found in it.
On maps, cartographers usually use several methods to portray the relief of the terrain. These include; contouring, layer tinting, relief shading, hachuring, benchmarks, trigonometric points, and spot heights. Which method is used on a certain map is usually the choice of the cartographer and a single map can contain more than one of these methods.
This article describes each of these methods in detail.

1. CONTOURING
Contouring is an act of using contour lines when representing the relief of an area on the map. 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).
Contouring is the most common method of showing relief on topographic maps. This is mainly because it has the ability to show all five (5) aspects of relief (shape, orientation, size, elevation, and slope) on the map.
Generally, the contour lines have the following characteristics;

i.                 They connect points of equal elevations above mean sea level.

ii.               They are numbered in either feet or meters, above sea level. Usually, these numbers represent the exact elevation of land above sea level for all points along that line.

iii.              Contour lines never cross or intersect each other. This is because it is impossible to have a point on the earth’s surface that can have two or more different elevations above sea level at the same time. However, the only exception for this is ‘overhanging cliffs’ where many contour lines merge to form one contour line.

iv.             The spacing or gap between the contour lines represents the degree of slope. Usually, closely spaced contour lines indicate a steep slope while contour lines far apart indicate gentle slope.

v.              Contour lines lie perpendicular to streams and rivers.

Contouring as a way of representing relief on the map has the following merits;

i.                     Contouring is the most suitable method of representing relief on large scale topographic maps.

ii.                   Contours provide the basis for other methods of representing relief such as layer tinting, hachuring, and relief shading.

iii.                 Contours can indicate the exact elevation of a point on the map.

iv.                 The distance between the contours may help to determine the slope of the land.

v.                   The shape and patterns that the contour lines make on the map can portray distinctive landforms such as hills, valleys, spurs, and cliffs.

The limitations of contouring include;

i.                     They are not suitable for representing relief on small-scale maps.

ii.                   Not all physical features and landforms can be portrayed by the contour lines. E.g. Coral reefs and outcrop rocks.

iii.                 The contour lines may fail to indicate some of the highest and important elevations on the map due to limitations of the vertical interval used.

This figure shows how contours are shown on maps. Notice how some of the contour lines are labeled with their elevations above mean sea level.

Read more about contours here: contour lines on topographic map

2. LAYER TINTING
Layer tinting, also known as layer coloring or hypsometric coloring is a method used to represent relief by using various shades of colors. In this method, the different elevations above sea level (and sometimes-below sea level) are represented on a map by a variety of colors. Usually, all areas on the map with relatively similar elevations will be represented by the same shade of color. 
A small range of colors is used but a wide range of different shades of these colors is used, to reinforce a better impression of the relief of the mapped area.
What color to be used at which elevation range is usually the choice of the cartographer. A cartographer may decide to use a cream color to represent lowland relief and increasing its intensity to light brown as the elevation increases, until on the highest elevations where he/she may decide to use the brown color. Meanwhile, another cartographer may decide to use a light green color to represent lowland relief and decreasing its intensity to a lighter brown color as the elevation increases until on the highest elevations where he/she may decide to use the white color. 
In this case, in order to avoid the confusion as to what color represents which elevation and to avoid misinterpretation of the relief, a layer tint box is usually printed on the map margin to indicate the elevation range represented by each color used on the map.

This figure shows a ‘layer tints’ box from one of East Africa’s Tanganyika 1960 series Y503 (Lushoto 1:50,000 topographic maps).

Maps that involve the system of colors to represent relief are known as ‘hypsometric maps’.
Layer tinting is the most suitable method of representing the elevation and shape of the relief on small-scale maps and it makes maps visually attractive and impressive to users. 
However, this method is characterized by many limitations, including;

i.                     It is not a complete method by itself since it relies on the contours to provide the basis for coloring

ii.                   It does not allow the map user to determine the exact elevation of a point, rather only gives the elevation range where the point might lie.

iii.                 This method is not applicable in the black and white maps.

iv.                 It is very expensive to produce a layer-colored map.

v.                   Colors carry certain ideas on people’s minds, hence one may easily misinterpret the map if not careful. For example; the green color may have been used to represent lowland relief on the map but a map user can misinterpret it thinking it represents vegetation cover.

3. HACHURING
Hachuring is one of the earliest methods used by cartographers to represent relief on the map. This method represents the relief of an area by using hachures. Hachures are short broken lines used on a map to indicate the direction and steepness of the slope. They do not represent exact elevations but are mainly used to give a good impression of the shape and slope of the ground.
Hachures usually vary in thickness and length. Thick and short hachures represent steeper slopes while thin and long hachures represent gentle slopes. The direction that these hachures point is the direction towards which the land is sloping.
Usually, hachures are applicable only in large-scale maps. They are not suitable for representing relief in small-scale maps. Despite the fact that the hachuring method is now used a little in cartography after being replaced by the contours, these two methods can sometimes be used together to make more emphasis on the relief of the mapped area.
The weaknesses of using this method include;

i.         Hachures do not show the exact elevation of points on the surface.
ii.         They are not applicable on flat or leveled land surfaces.
iii.        For cartographers, the preparation of hachures is exhaustive and time-consuming since they are hand-made.
iv.        Too many hachures on the map can obscure other map detail.

This figure shows how hachures are depicted on topographic maps. Notice how the hachure lines in both (a) and (b) differ in thickness, length and direction.

3. RELIEF SHADING
This method uses ‘light and shadows’ to highlight the three-dimensional appearance of terrain on maps. Cartographers normally follow the principle of ‘top-left lighting’ when employing the technique of relief shading to show relief on the map. The relief would appear as if there is a light source illuminated at the top-left corner of the map, giving the map a light-shadow effect.
In this method, the illuminated parts of the relief are shown by lighter shades and the obscured parts of the relief are shown by darker shades. On the obscured parts of the relief, the slope is darkened according to its steepness (i.e. The steeper the slope, the darker the shade), whereas, on the illuminated parts of the relief, the slope is shown by progressively lightening the shades.
The variation in shadowing gives the map a 3D effect and helps put into context how hilly or flat the area mapped is.
The main downside of using this method is that it does not show the exact elevation of the relief features on the map.

This figure shows two topographic maps. The map on the top shows the area around Lake Mead in the U.S. The map on the bottom shows the same map with shaded relief. Notice how contour lines are used to represent relief on the map on top, but on the bottom map, both relief shading and contour lines are used in order to make more emphasis on the relief of the mapped area.

5. ELEVATION POINTS
Elevation points are miscellaneous dots and marks used to show the elevation of a certain point on the map.  The three main types of elevation points used on the map are trigonometric points, spot heights, and benchmarks.

A. TRIGONOMETRIC POINTS

Trigonometric points are conventional small triangles used on maps to show the exact elevation of the highest point in a given area. Trigonometric points are depicted on the map by small triangles together with a number which indicates the exact elevation of the given point on the map.

Surveyors carefully choose trigonometric stations because they help to provide the basis of surveying in an area by forming corners of intersection of carefully measured triangles in a given field. The surveyors usually erect a concrete pillar on the highest point in a field, which acts as the corner of the main triangle of the survey. The areas where these pillars are erected are known as trigonometric stations. Thus, a trigonometric point on a map indicates the presence of a trigonometric station on the ground.

On maps, trigonometric points can either be primary, secondary or tertiary. Primary trigonometric stations show the highest points in the area mapped, secondary trigonometric stations show high points in the area mapped but they are usually at a lower elevation than the primary stations and tertiary trigonometric stations show other stations in the area mapped.

This figure shows the three kinds of trigonometric points used on maps; (a) primary trigonometric point at the elevation of 4282m above mean sea level, (b) secondary trigonometric point at the elevation of 1447m above  mean sea level, and (c) tertiary trigonometric point at the elevation of 766 m above  mean sea level.

The use of trigonometric points on maps to represent relief has the following merits;

i.                     They enable the map user to easily recognize the highest elevation in a given area.

ii.                   They show the highest elevation in an area which cannot be shown but contours due to the limitation of vertical interval.

iii.                 They can be used without obscuring other features.

iv.                 They have physical evidence on the grounds they appear in. A trigonometric point on a map indicates the presence of a trigonometric station on the ground.

B. SPOT HEIGHTS

Spot heights (also called spot elevations) are conventional dots used to show the exact elevation of points on the map. They are used to indicate the elevation of the ground at ruling points on the surface such as the top of hills.

Spot heights are depicted by using a dot together with a number which indicates the exact elevation of the given point on the map.

However, unlike trigonometric points, spot heights do not have physical evidence in the fields they appear.

This figure shows how spot elevations are shown on maps. It means that the given spot height is at the elevation of 2802 meters above mean sea level.

The use of spot heights has the following advantages;

i.                     They provide accurate elevation of given points on the map.

ii.                   They may be used to show a point of higher elevation which cannot be shown by contours due to the limitation in the vertical interval.

iii.                 The methods can be easily used without obscuring other features.

The limitations of using spot heights include;

i.                     They do not provide much information about the relief of the land.

C. BENCHMARK
A benchmark is a surveyor’s mark, which is made on a stationary object on the ground like a wall, a pillar, a rock or a building whose position and elevation have been (previously) determined/ are known.
Benchmarks are also useful in map analysis since they show the exact elevation of a given point on the map. In surveying, they are used as reference points from which the elevations of other objects on the ground are determined. 

On maps, it is usually indicated by a dot followed by the elevation value of the given point on the map together with letters BM.

This figure shows how benchmarks are shown on maps. It means that the given benchmark is at the elevation of 1250 meters above mean sea level.

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