Geographic Grid: Latitudes & Longitudes PDF

Geographic Grid: Latitudes and Longitudes 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 any place on the earth's su...

Geographic Grid: Latitudes and Longitudes 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 any place on the earth's surface. These criss-crossing lines form a framework known as the Geographic Grid. 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 (23% N) is a line of latitude located 23° north of the Equator. The Tropic of Capricorn (232°S) is a line of latitude located (232°S) south of the Equator.  The Arctic Circle represents 66°N latitude. The Arctic Circle marks the limit of the north polar region surrounding the North Pole. The Antarctic Circle represents 66°S latitude. 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 length of the Equator is equal to the circumference of the earth or 40,077 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. 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 area 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 (23½°N) and Tropic of Capricorn (23½°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 (662°N) and the Antarctic Circle (662°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 (232°N to 662°N) and the South Temperate zones (232°S to 66°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. LINES OF LONGITUDE A longitude is the 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. 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 meridianum meaning noon. 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. Thus 0° and 180° meridian together make a full circle round the earth. The two diametrically opposite lines make a full circle also known as the Great Circle. The distance between two lines of longitude is maximum at the Equator (111 km). The distance decreases gradually as one moves towards the poles. LONGITUDE AND TIME The lines of longitude, as stated earlier, are also known as the 'Meridians'. At a particular moment of time, if it is 12 Noon at a given longitude, it must be 12 Noon at all places on this longitude. For the purpose of memorising, EGA-WLS formula is used. EGA stands for East Gain Add and WLS stands for West Lose Subtract. Eastern and Western Hemisphere The Prime Meridian, together with the 180° longitude usually divides the earth into the Eastern and Western Hemispheres. This division holds good practically for all purposes. However, any two diametrically opposite lines can also divide the earth into two equal hemispheres. LOCAL TIME The local time of any place is obtained by the overhead sun at noon. TIME ZONES AND STANDARD TIME Time Zones To overcome the confusion while allowing the interplay of natural forces to operate, the earth has been divided into 24 Time Zones according to the number of hours in a day! Each zone covers 15° longitude. Standard Time The uniform time based on a central meridian is known as the Standard Time. Greenwich Mean Time The time at Greenwich (0° longitude) has been selected as the mean time. The time fixed with reference to Greenwich is called the Greenwich Mean Time of GMT. Indian Standard Time (IST): In our country, 82°30'E is the central meridian. It passes through Mirzapur near Allahabad (Prayagraj). It is known as the Standard Meridian of India. INTERNATIONAL DATE LINE: The line of longitude 180° is one and the same for East or West of the Prime Meridian. The International Date Line (IDL) is the 180° line. When crossing this date line from the west to east a day is deducted or the time is fixed backward by one day. When crossing the IDL from east to west, a day is added, or the calendar is fixed one day ahead. To avoid the confusion of having different dates within the same country, the Date Line bends and goes Zig Zag. LOCATING PLACES With the help of the grid, we can locate places on the globe or the map, if we know the latitude and longitude of those places. Worked Out Examples The latitude and longitude of three places is given below. Pinpoint these places on the globe. (i) New York = Latitude 41°N and Longitude 74°W (ii) New Delhi = 30°N and 77°E (iii) Mumbai = 19°N and 73°E GREAT AND SMALL CIRCLES A great circle is a circle that is drawn on the surface of a sphere (such as the earth) that has a radius equal to the radius of the sphere. Circles which do not pass through the centre of the earth are the small circles. Characteristics of a Great Circle (i) A great circle is a theoretical circle formed. (ii) All such circles must pass through or touch the centre of the circle. (iii) Infinite number of circles that touch the two opposite ends of the sphere can be drawn on a sphere. (iv) Intersecting great circles always bisect each other. Uses of Great Circles (i) Navigators use great circles to find the shortest distance between any two. points on the earth's surface. A Great Circle Route is the shortest distance between two places on the earth and lies on the arc of a great circle. (ii) Great Circle routes are specially important for places that are on opposite sides of the globe. Most globes show great circle routes between distant ports across the Atlantic, the Pacific and the Indian Ocean. (iii) Great circles are used by meteorologists to determine climate and weather conditions in a region.