ICSE Class 6 Geography Chapter 2 Geographic Grid Latitudes and Longitudes

Chapter Two

Geographic Grid: Latitudes and Longitudes

Syllabus

Geographic Grid: Latitudes and Longitudes

(a) Concept of latitudes: main latitudes, their location with degrees, parallels of latitude and their uses.

(b) Concept of longitudes - Prime Meridian, time (local, standard and time zones, Greenwich Mean Time (GMT) and International Date Line (IDL). Eastern and Western hemisphere.

(c) Using latitudes and longitudes to find location. Calculation of time.

(d) Great Circles and their use.

Geographic Grid

The earth's surface is so vast that unless a mathematical method is used, it is impossible to locate a place on it. For this reason, imaginary lines are drawn on the globe. The lines running east to west, parallel to the Equator, are called lines of latitude. The lines running north to south passing through the poles are called lines of longitude. The intersection of latitudes and longitudes pinpoint a place on the earth's surface. These cross-crossing lines form a framework known as the Geographic Grid.

Eratosthenes, the Greek philosopher, who had for the first time calculated the circumference of the earth, had devised lines of latitude and longitude to locate places on the earth.

This grid on the globe or the map serves the same purpose as the system of coordinates on the x-axis and y-axis on a graph paper.

In this case the x-axis is represented by lines of latitude (horizontal) and y-axis, by lines of longitude (vertical).

Lines of Latitude

Lines of Latitude are the imaginary lines joining all places having the same latitude towards north or south of the Equator.

A latitude is the angular distance of a place north or south of the Equator.

A latitude is marked in degrees, with Equator being 0 degrees.

Latitudes are calculated according to the angle a place makes with the centre of the earth.

Since the lines of latitude are parallel to the Equator and each other, they are called parallels of latitude.

Each parallel of latitude is a full circle. However, only the Equator is a Great Circle.

Main Latitudes

There are 181 parallels of latitude at 1° interval.

Equator is the longest line of latitude. It represents 0° latitude.

The North Pole (90° N) is located at an angular distance of 90° north of the Equator.

The South Pole is located at an angular distance of 90° south of the Equator.

The Tropic of Cancer (231/2°N) is a line of latitude located 231/2° north of the Equator.

The Tropic of Capricorn (231/2°S) is a line of latitude located 231/2°S south of the Equator.

The Arctic Circle represents 661/2°N latitude. The Arctic Circle marks the limit of the north polar region surrounding the North Pole.

The Antarctic Circle represents 661/2°S latitude. The Antarctic Circle marks the limit of the south polar region around the South Pole.

Northern and Southern Hemisphere

The Equator that runs midway between the poles divides the earth into two equal hemispheres known as the Northern Hemisphere and the Southern Hemisphere.

The Poles-North Pole and South Pole-are opposite to each other at the extreme ends of the sphere. They are each located at 90° angular distance north or south of the Equator.

The length of the Equator is equal to the circumference of the earth or 40,075 km. Since the circumference of a circle is equal to 360°, the 1° angular distance is roughly equal to 111 km.

Uses of Latitudes

The lines of latitude form one of the coordinates of the grid system. The lines of latitude have the following uses:

To find the location of a Place: Latitudes give us the location of a place north or south of the Equator. Such a location is known as an absolute location.

To measure the distance of a Place: Distances are calculated with reference to the Equator at right angle to the place. We can therefore, measure the distance of any place from the Equator based on its degree of latitude. For example, the latitude of Mumbai is 19°N and that of New Delhi is 30°N. We know that Mumbai is 111 × 19° away from Equator. Similarly, New Delhi is 3,330 km (111 × 30°) away from Equator.

Heat Zones: Besides helping us to locate places on maps and charts, lines of latitude divide the earth into distinct heat belts. The lines of latitude indicate the general climate of the region. By applying the principle of heat zones or thermal zones of the earth. Thus, latitudes enable us to divide the whole earth into different climatic zones.

The Torrid or Tropical Zone: The area lying between the Tropic of Cancer (231/2°N) and Tropic of Capricorn (231/2°S) mark the limits of the Torrid (meaning very hot) Zone. It is also called the Tropical Zone. It is the hottest zone of the earth.

The Temperate Zones: Two other important lines of latitude based on temperature are the Arctic Circle (661/2°N) and the Antarctic Circle (661/2°S). Between the Arctic Circle and the Tropic of Cancer as well as between the Antarctic Circle and the Tropic of Capricorn lie the two Temperate Zones - the North Temperate (231/2°N to 661/2°N) and the South Temperate zones (231/2°S to 661/2°S). In this region, the climate is moderate, i.e., neither too hot nor too cold.

The Frigid Zones: Between the Arctic Circle and the North Pole and between the Antarctic Circle and the South Pole are the two Frigid Zones of the earth. These are the polar regions and receive the sun's slanting rays. In these two zones, very low temperatures are recorded.

Teacher's Note

Understanding latitude helps us know why cities near the equator are hotter while polar regions are colder - something you can observe in weather patterns of places you follow or travel to.

Lines of Longitude

A longitude is angular distance of a place east or west of the Prime Meridian.

The Prime Meridian is the line of longitude whose angular distance is defined as 0°. It passes through Greenwich near London.

The lines to the west of Greenwich are suffixed with 'W' and those east of Greenwich are suffixed with 'E'. For example 60°W and 60°E.

There are a total of 360 lines at 1° interval.

The lines of longitude are also called Meridians of Longitude. 'Meridian' is derived from the Latin word meridianus meaning noon. The sun crosses a meridian at noon. All places on a particular meridian will have noon at the same time.

All meridians of longitude converge at the poles and are thus of equal length.

The Prime Meridian is numbered as 0°. The others are numbered between 0° to 180°E or W. The line 180°E and W refer to the same meridian. It is diametrically opposite to the 0° longitude. Thus 0° and 180° meridian together make a full circle round the earth. Proceeding at 1° interval from both East and West, other full circles will be 1°- 179°, 2°- 178°, 60°- 120° and so on. Of the two lines of longitude that are diametrically opposite, one will be in the east and the other in the west. The sun total for each meridian at every 1° longitude is different. It is said that, if it covers every 1° longitude in degrees. Thus, if it is 12 Noon at 0° longitude, it must be 4 minutes past 12° Noon towards the east at the end 1° longitude or 15°E longitude, it must be 1 p.m. Towards the west, it will be 1 hour less because the Earth rotates from West to East.

Teacher's Note

Longitude helps us understand why when it's noon in New York, it's evening in London - the earth's rotation creates different times across the globe.

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