Geographical Grid – Latitude & Longitude – Geography Notes

The Geographical Grid-Latitude & Longitude

• Latitudes and Longitudes are imaginary lines used to determine the location of a place on Earth.
• The shape of the earth is ‘Geoid’. The location of a place on the earth can be mentioned in terms of latitudes and longitudes. Example: The location of New Delhi is 28° N, 77° E.

Earth Latitude

• Latitude is a geographical coordinate that is used to specify a location’s position on the Earth’s surface.
• It is measured in degrees, minutes, and seconds, and it represents the angular distance between the point of interest and the Equator. 
• The Equator is an imaginary line that circles the Earth’s circumference and divides it into two hemispheres – the Northern Hemisphere and the Southern Hemisphere.
• For example at the equator (0°) it is 68.704 miles, at 45° it is 69.054 miles and at the poles it is 69.407 miles. The average is taken as 69 miles (111km).
• 1 mile = 1.607 km.

Important parallels of latitudes

• Besides the equator (0°), the north pole (90°N) and the south pole (90° S), there are four important parallels of latitudes–
  • Tropic of Cancer (23½° N) in the northern hemisphere.
  • Tropic of Capricorn (23½° S) in the southern hemisphere.
  • The Arctic circle at 66½° north of the equator.
  • Antarctic circle at 66½° south of the equator.
• The parallels or lines of latitude are circles that are parallel to the Equator and are measured in degrees north or south of the Equator. 
• The Equator itself is at 0 degrees latitude, and the North Pole and South Pole are at 90 degrees north and 90 degrees south latitude, respectively. 
• The lines of latitude are used in conjunction with lines of longitude, which run from the North Pole to the South Pole and are used to specify a location’s position east or west of the Prime Meridian.
• If parallels of latitude are drawn at an interval of one degree, there will be 89 parallels in each hemisphere, for a total of 178 parallels. However, we should also include the equator as a parallel, which brings the total number of parallels to 179.
• At the equator, it is 110.6 km and at the poles, it is 111.7 km.
• The latitude of a place may be determined with the help of the altitude of the sun or the Pole Star.

Latitudinal Heat zones of the earth

• The area between the Tropic of Cancer (23.5 degrees north latitude) and the Tropic of Capricorn (23.5 degrees south latitude) is known as the tropics or the tropical zone. The region within this zone where the sun is directly overhead at least once a year is known as the torrid zone or the equatorial region.
• The mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun’s rays goes on decreasing towards the poles. As such, the areas bounded by the Tropic of Cancer and the Arctic circle in the northern hemisphere, and the Tropic of Capricorn and the Antarctic circle in the southern hemisphere, have moderate temperatures. These are, therefore, called temperate zones.
• The areas beyond the polar circles in both the Northern and Southern Hemispheres are known as the frigid zones. These regions are extremely cold due to the low angle at which the sun’s rays hit the Earth’s surface, resulting in less solar radiation being absorbed by the surface. In the frigid zones, the sun remains low on the horizon for most of the year, and during the winter months, there may be periods of continuous darkness. 

Earth Longitude

• Longitude is an angular distance, measured in degrees, between a point on the Earth’s surface and the Prime Meridian, which is an imaginary line running from the North Pole to the South Pole and passing through the Royal Observatory in Greenwich, London.
• The meridians of longitude are semicircles that converge at the poles. If opposite meridians are taken together, they complete a circle, but they are valued separately as two meridians.
• The Prime Meridian, which passes through the Royal Observatory in Greenwich, London, is the line of longitude that marks the 0° point on the globe.
•  From this line, all other lines of longitude, also known as meridians, are measured eastward and westward up to 180°.
• The distance between two lines of longitude is smallest at the poles, and widest at the equator.
• Time zones are regions of the Earth where the same standard time is used. 
• They are defined by the difference in hours from Greenwich Mean Time (GMT), which is based on the Earth’s rotation and is used as a reference time for the entire world.
• The Eastern Hemisphere includes all land and water located to the east of the Prime Meridian, while the Western Hemisphere includes all land and water located to the west of the Prime Meridian.
• Measured also in degrees, minutes, and seconds, longitude is the amount of arc created by drawing first a line from Earth’s center to the intersection of the Equator and the prime meridian and then another line from Earth’s center to any point elsewhere on the Equator.
• The distance per degree of longitude at the Equator is about 111.32 km (69.18 miles) and at the poles, 0.  

Longitude and Time

• Since the earth makes one complete revolution of 360° in one day or 24 hours, it passes through 15° in one hour or 1° in 4 minutes.
• The rotation of the Earth on its axis is what causes the cycle of day and night, and it takes approximately 24 hours or one day to complete a full rotation.
• The Earth rotates at a rate of 15 degrees of longitude per hour, or one degree of longitude every four minutes.
• As 180° of longitudes fall both east and west of the Prime Meridian, the sun thus takes 12 hours’ time to traverse the eastern and western hemispheres.
• We may thus conclude that places east of Greenwich see the sun earlier and gain time, whereas places west of Greenwich see the sun later and lose time.
• The rate at which the sun traverses over certain degrees of longitude is used to determine the local time of a particular area with respect to the Prime Meridian (0 degrees longitude).
• If we know G.M.T., to find local time, we merely have to add or subtract the difference in the number of hours from the given longitude.

Meridians

• Prime meridian
• International Dateline

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