The Earth in Relation to the Universe
Senior 1 · Geography
The Earth in Relation to the Universe
Lesson 3 of 4
22 min
Kigali's position can be written as 1°57′S, 30°04′E. With just these two numbers, a pilot in Addis Ababa, a ship's captain in the Indian Ocean or a phone anywhere in the world can find the city. In Unit 2 you used a grid on one map. Latitude and longitude are a grid drawn over the whole Earth.
Figure 1. Latitude lines run east–west and measure distance north or south of the Equator; longitude lines run pole to pole and measure distance east or west of the Prime Meridian.
Definition
Latitude: the distance of a place north or south of the Equator, measured as an angle in degrees from the centre of the Earth, from 0° at the Equator to 90°N or 90°S at the poles. Lines of latitude are called parallels. Example: Kigali is at latitude 1°57′S.
Definition
Longitude: the distance of a place east or west of the Prime Meridian, measured as an angle in degrees, from 0° to 180°E or 180°W. Lines of longitude are called meridians and run from pole to pole. Example: Kigali is at longitude 30°04′E.
Definition
Equator: the line of latitude 0°, a circle round the middle of the Earth halfway between the poles. It divides the Earth into the northern and southern hemispheres. It is the longest line of latitude, about 40,075 km round.
Definition
Prime Meridian: the line of longitude 0°, which passes through Greenwich in London. It and the 180° meridian opposite it divide the Earth into the eastern and western hemispheres.
| Latitude (parallels) | Longitude (meridians) | |
|---|---|---|
| Direction of the lines | East–west, round the Earth | North–south, pole to pole |
| Starting line (0°) | The Equator | The Prime Meridian (Greenwich) |
| Largest value | 90°N and 90°S (the poles) | 180°E and 180°W (the same line) |
| Length of the lines | Shorter towards the poles; the Equator is longest | All the same length; they meet at the poles |
| Spacing | Parallel: always about 111 km per degree | About 111 km per degree at the Equator, closing to 0 at the poles |
| Used for | Position north–south; climate zones | Position east–west; time zones (Lesson 4) |
Five parallels have special names: the Equator (0°), the Tropic of Cancer (23½°N) and Tropic of Capricorn (23½°S), where the noon Sun can be overhead, and the Arctic and Antarctic Circles (66½°N and S). Each degree is divided into 60 minutes (′), so 1°30′ means one and a half degrees.
Worked example 1: writing a position
A GPS phone app shows Kigali as , . Write this in degrees and minutes.
Step 1. Latitude. The minus sign means south. Keep the 1°, and change the decimal part to minutes: . Latitude = 1°57′S.
Step 2. Longitude. Positive means east. . Longitude = 30°04′E.
Answer. 1°57′S, 30°04′E. Always write the latitude first, and never forget the letter (N, S, E or W).
Worked example 2: distance from the Equator
Along a meridian, each degree of latitude is about 111 km. How far is Kigali from the Equator?
Rwanda runs from 1°03′S to 2°50′S, a difference of 1°47′ (1.78°), so the country is about km from north to south.
Figure 2. Rwanda's latitude and longitude. The red dashed lines mark the country's most northerly, southerly, westerly and easterly points. Outline from Natural Earth.
Important
Case study: what Rwanda's latitude and longitude tell us
Longitude and Latitude Explained, by ClickView (3 min). Watch how the two sets of lines are combined to give one exact position, and notice which number is given first.
Kigali and Quito (the capital of Ecuador, in South America) are both very close to the Equator. What would you expect them to have in common, and what might be different? Consider day length, the height of the Sun, altitude and time of day.
Tip
LAT is FLAT: lines of latitude lie flat, like the rungs of a ladder you climb north or south. LONG lines are LONG: they stretch from pole to pole. Always give latitude first: "lat before long", like "ladder before lane".
Practice
Remember
Sources and credits
The lesson text, globe diagrams, map, table, worked examples and practice are written by Ganzaa. Rwanda's extreme latitudes and longitudes are from the Wikipedia article "Geography of Rwanda" (CC BY-SA 4.0).
