Elements of a Map
Senior 1 · Geography
Elements of a Map
Lesson 4 of 4
25 min
A map is flat, but Rwanda is anything but flat. How can a sheet of paper show a hill, a valley or a steep slope? Look at the picture below: it is a topographic map laid over a three-dimensional model of the land it describes.
A map cannot show every house and tree as it really looks, so it uses symbols: small drawings, lines, letters and colours that stand for features. Most topographic maps follow the same colour habits: blue for water, green for vegetation, brown for relief (contours), and black or red for things people have built.
| Symbol | Feature | Symbol | Feature |
|---|---|---|---|
| Main (tarmac) road | School | ||
| Earth (murram) road | Church | ||
| Footpath | Mosque | ||
| River | Health centre | ||
| Lake or pond | Contour line with its height | ||
| Swamp or marsh | Spot height (in metres) | ||
| Forest | Trigonometrical station | ||
| International boundary |
Symbols differ from one map series to another, so always read the key of the map in front of you.
Definition
Map symbol (conventional sign): a drawing, line, letter or colour used on a map to stand for a real feature, explained in the key. Example: a blue wavy line for a river; a cross for a church.
Height on a map is shown in three main ways: spot heights (a dot with the height written beside it), trigonometrical stations (survey points marked by a triangle, whose height is known exactly), and contour lines.
Definition
Contour: a line on a map joining places that are at the same height above sea level. Example: every point on the 1,600 m contour is exactly 1,600 m above sea level.
Definition
Contour interval: the difference in height between two neighbouring contour lines on a map; it is the same all over one map. Example: in Figure 2 the contours are 1,500, 1,550, 1,600 m and so on, so the contour interval is 50 m.
Definition
Spot height: a dot on a map with a number beside it giving the exact height of that point above sea level. Example: the summit in Figure 2 has a spot height of 1823, meaning 1,823 m.
Figure 2. A contour map of a hill (top) and the cross-section along the line A–B (bottom). The vertical scale is stretched so the shape is easy to see.
Worked example
Worked example 1: drawing the cross-section A–B (Figure 2)
Step 1 Lay the straight edge of a strip of paper along A–B. Mark A, B and every point where a contour crosses the edge, writing the height beside each mark.
Step 2 Draw a horizontal base line the same length as A–B, and a vertical scale beside it (in Figure 2, from 1,450 m to 1,850 m).
Step 3 Lay the strip along the base line and, above each mark, plot a dot at its height.
Step 4 Join the dots with a smooth curve, rising to the summit (1,823 m) between the two 1,800 m points. Shade the land below the line, and label A, B and the heights.
Reading it. From A the land climbs 300 m over a long distance: a gentle slope. East of the summit it falls about 320 m to the 1,500 m contour in a much shorter distance: a steep slope. This matches the spacing of the contours.
Worked example 2: finding the contour interval
On a map, two labelled contours read 1,600 m and 1,700 m, and there are four unlabelled contours between them. What is the contour interval?
Four lines between them divide the 100 m into five equal steps:
Warning
Count the gaps, not the lines. With four lines between two labelled contours there are five gaps. Dividing by four is the most common mistake.
Important
Case study: contour lines on Rwanda's hills
Rwanda's farmers draw "contours" with their hoes. On steep hills, fields are cut into terraces that follow the contour, and hedges and grass strips are planted along the contour too. Rain that falls on a level terrace soaks in, instead of rushing down the slope and washing the topsoil into rivers such as the Nyabarongo. Where a topographic map shows contours packed tightly together, planners know the slope is steep and that terracing, tree planting or leaving the land under forest will be needed.
Understanding contour lines, with Steve Backshall and Ordnance Survey (1 min). Watch how the lines are imagined as the edge of water rising up a hill, one level at a time.
A sketch map is a simple map drawn by hand to show the main features of an area, for example the way from your home to school. It is not measured exactly, but it must still be clear and complete.
Figure 3. A model sketch map. It is not to scale, but it still has a title, frame, key and north arrow.
Definition
Sketch map: a map drawn freehand, without exact measurement, to show the main features of an area and where they are in relation to each other. Example: Figure 3.
Look at the terraces in the photograph. A new road must be built up this hill. Should it go straight up the slope or follow the contours? Use what you know about contours and the case study to argue your choice.
Tip
Close = climb. Where contours are close together you would be climbing hard; where they are far apart you could walk easily. For a sketch map, remember "FT-NK": Frame, Title, North arrow, Key.
Practice
Remember
Further reading
Books and resources for this unit
Sources and credits
The lesson text, symbol table, contour map and cross-section, sketch map, worked examples and practice are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
