Locating features on a map: latitude and longitude

Introduction

Two of the most fundamental questions in geography are 'where is it?' and 'where am I?' Since ancient times, people have been interested in identifying exactly where things are located in the world. The Earth, however, is a sphere, which means that it has no edges, and, therefore, no top or bottom. This has made it very difficult for people to explain, define or measure their position. A coordinate system, involving imaginary lines which span around the world, was eventually developed to solve this problem. This was the system of latitude and longitude.

Latitude

Lines of latitude are horizontal lines which run from east to west across the world. Since each of these lines is parallel (run in the same direction and are equidistant at all points), they are often called parallels of latitude. While these lines appear straight when looking at a map, they span around the entire of the world to form circles. This is why they are sometimes referred to as circles of latitude. Circles of latitude are not all the same size. The largest circles are located closest to the equator. The circles become smaller the closer they are to the North and South Poles.

Lines of latitude are measured in degrees (written as ^o). Latitudinal lines are given a number between 0^o and 90^o. They are essentially measurements of angles. These angles are most easily calculated by imagining the Earth being horizontally cut in half. For greater accuracy, degrees marking the angular measurements of the Earth can be sub-divided into minutes (written as ') and seconds (written as "). There are 60' (minutes) for every 1^o (degree) and 60" (seconds) in every 1' (minute). In the real world, 1^o of latitude is equivalent to between 59.70 nautical miles at the equator and 60.31 nautical miles near the North and South Poles. These distances equate to between 110.57 and 111.69 kilometres on land.

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There are a number of important lines of latitude. Since lines of latitude give the location of a place in terms of being north (N) or south (S) of the equator, the most important line is the equator. The equator, which is located half way between the North Pole (90^o N) and South Pole (90^o S), is measured at 0^o. The equator divides the world into halves. Any place which is located above the equator is said to be in the Northern Hemisphere and any place below the equator is known as being in the Southern Hemisphere.

There are four other important lines of latitude. They are: the Arctic Circle (66^o 33' 39" N), the Tropic of Cancer (23^o 26' 22" N), the Tropic of Capricorn (23^o 26' 22" S) and the Antarctic Circle (66^o 33' 39" S).

Longitude

Lines of longitude are vertical lines which run from north to south on the Earth. Each line extends from its starting point at the North Pole, to its finishing point at the South Pole. These lines form large semi-circles of equal size. These lines are also called meridians of longitude.

Lines of longitude are measured in degrees and minutes, in the same way that lines of latitude are. While lines of latitude do not exceed 90^o north or south, however, lines of longitude can extend to 180^o east or west. Lines of longitude are also not of equal distance from each other at all points along the line. They resemble slices of an orange, which are thicker in the middle and thinner at each end. This means that the lengths of degrees of longitude are not equal, or not even similar like the latitudinal lengths of degrees. While the distance between degrees of longitude is around 59.97 nautical miles (111.06 kilometres on land) at the equator, the number of nautical miles in a degree greatly decreases as the lines become closer to the North and South Poles.

The most important line of longitude is the Greenwich Meridian (also known as the Prime Meridian). In 1884, the Greenwich Meridian, which runs through Greenwich in England, was adopted as the universal zero point of longitude. The Greenwich Meridian divides the world into an Eastern and Western Hemispheres. The lines of longitude in the east (E) are sometimes written as plus (+) degrees and those in the west (W) are sometimes referred to as minus (-) degrees.

Aside from identifying location, longitudinal lines also assist in telling world times. The world is divided into 24 time zones. Each zone is based on the lines of longitude, at intervals of 15^o apart. The International Date Line, which represents the change of day, is at a longitude of 180^o.

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Finding places

When looking at the index of an atlas, all places will have a reference of longitude and latitude. The New South Wales city of Orange has a latitude of 33^o 16' S and a longitude of 149^o 06' E. In order to locate Orange on the map, the first step a student should take is to look at which hemispheres it is situated in. The reference tells us that Orange is located south of the equator and east of the Greenwich Meridian.

The second step involves the student reading the degrees of latitude and longitude written along the side of the map. To find Orange, the student should travel along the horizontal lines of latitude to find 33^o. While still looking at that same point, the student should then travel directly up or down the vertical lines of longitude to find 149^o.

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