Mugisha and Mucyo are traders in Kigali and they export goods made in Rwanda and import some missing commodities not locally produced. Sometimes goods delay as they are being transported from Mombasa port. Suppose you want to travel with these traders, explain how you would use a map to find out the distance from Kigali to Mombasa

Bearing is an accurate way of giving the direction of one place in relation to another. It is more accurate than direction because it has 360 points compared to the 16 points of a compass. Instead of saying, for example, that place A is north east of place B, we use degrees. So, we would say that place B is situated at 045° from place A. The bearing of a point is the number of degrees in the angle measured in a clockwise direction, from the North line to the line joining the centre of the compass with the point. This is illustrated below :

true bearing中文

A grid is a series of straight lines drawn vertically and horizontally on topographical maps. Where the lines cross each other to form squares of equal sizes. The lines running from north to south (vertical lines) are called Eastings. This is because their numbers increase towards the east from the south western corner. This corner is known as the grid origin and it is from it that all readings start. There are those drawn horizontally, and their numbers increase towards the north. These are called the Northings.

Hachures are short lines on a map that indicate the direction and steepness of a slope. Hachures that represent steep slopes are short and close together while hachures that represent gentle slopes are longer, lighter, and farther apart.

Bearing Math

A map is a representation of the actual ground on a piece of paper. It is usually drawn to scale. Distance on the map is measured between two points, e.g. between a school and the museum or any other feature. Then, the distance measured on the map is converted into the actual distance on the ground. The distances can either be straight or curved. To measure the distance requires:

The value of the easting (vertical gridline) is read first, followed by the value of the northing (horizontal Gridline). The values of the Eastings and northings are known as coordinates. The coordinates are expressed as a single continuous figure without decimal points or commas, for example, 646 504 and not 64, 65, 04. They are plain numbers, without units of measurement.

Contours are lines that join places of the same height above the sea level. A contour is represented in brown lines on the topographical maps. The height of the contour is indicated on each contour line. The difference between one contour line and the next is called contour interval. If only certain contours are numbered, one must find how many contours lie between the numbered contours and work out the contour interval. A contour interval is given on the legend on the topographical maps. From the below illustration, the contour interval is 20 m.

The surface of the earth is not flat. It has such features as mountains, valleys, gullies, hills, plateaus and plains. In Geography, this form of landscape is called relief. In other words, relief is the general appearance of the land’s surface. It does not include the aspects covered in human geography. The following are the most common techniques used to represent relief features:

On a bearing of

An area is calculated to determine the actual (size on the ground) of a feature / region / demarcated area. The area of a feature can be regular or irregular in shape.)

A map scale refers to the relationship (or ratio) between distance on a map and the corresponding distance on the actual ground. The map scale tells you about the comparative size of features and distances displayed on the map.

The bearing of A from B

The lines shown on the illustration above, intersect forming grid squares. These are formed by both vertical lines (Eastings) and Horizontal lines (Northings). These are called grid references or geographical coordinates. They are the ones that are used to locate places and features indicated on the map. This is illustrated hereunder:

On topographical maps of the scale 1:50,000, there are grid squares measuring 2 cm by 2 cm. On the ground, these measure 1 km by 1 km. This means that they have an area of 1 km2. To calculate the area of irregular shapes,

Key unit competency: By the end of this unit, I should be able to measure the bearings and the directions, calculate distances and areas on a map.

Altitude is the height above sea level. It is the height of a point in relation to the seal level. Elevation is the vertical distance above the sea level while Height is the vertical distance from the base to the top. The figure below shows how relief is determined.

Bearing angle

Direction is the relative position of a place from another using the points of the compass. The main cardinal points of a compass are north, east, south and west. The first letters of these directions (in capital) are used in place of the full names. These are N—North, E—East, S—South and W—West.

A bearing is used to represent the direction of one-point relative to another point. For example, the bearing of A Form B is 245˚. The bearing of B from A is 065˚. Bearing is also the direction to something measured as an angle relative to the north. It increases towards the East, with North=0 degrees, East=90 degrees, South=180 degrees, and West=270degrees.

The dark lines with reading are index contour lines while thin lines represent intermediate contours. The difference in height or altitude between two places is known as the vertical rise or the vertical interval (V.I.).

Hill shading is the method of adding light and dark area or shading to a map to highlight the location of hills or mountains. When light is shone from a given direction, areas with steep slopes are hidden. Such parts can be clearly shown by shading. The thickness of the shade depends on how steep the slope is. Steep relief has darker shading compared to gentle slopes. This method does not show the exact height of the relief feature. Refer to the figure below.

Colouring or layer tinting is a method of showing relief by colour. A different colour is used for each band of elevation. Each shade of colour or band, represents a definite elevation range. A legend is printed on the map margin to indicate the elevation range represented by each colour. However, this method does not allow the map user to determine the exact elevation of a specific point; only the range is identified.

Compass bearing

The four-figure grid reference has four digits. It gives the grid square in which a position is found. The four-figure grid reference of Yellow Square in figure 2.31 below is found as follows:

This reference has six digits. It is more exact than the four-figure grid reference. To get the six-figure grid reference for red square in figure 2.32 below, the following is done:

A spot height is shown as a dot and the actual height in metres. Spot heights are mainly used where drawing of complete contours is difficult. This happens on such features as mountain peaks and hilltops. Trigonometrical stations are also known as triangulation points. Surveyors mark those using triangles or circles with a dot at the centre.

Imagine someone comes from Europe to visit Rwanda, specifically in Muhoza sector, Musanze district (see the map below). At Kigali airport someone gives him a map with a scale of 1:50 000. He/ she needs to know the bearing of Muhoza from Kigali.

In this method, certain symbols are used to show relief on maps. It does not give the heights above sea level. Only a small variety of landforms can be shown using it. The pictures may further hide important details. See the figure below.