Longitudes and Latitudes

• The earth's surface is so vast that unless a mathematical method is used, it is impossible to locate a place on it
• Geographic Grid


  Imaginary lines drawn on the globe, including lines of latitude running east to west parallel to the Equator, and lines of longitude running north to south passing through the poles
• The intersection of latitudes and longitudes pinpoint a place on the earth's surface
• Eratosthenes, the Greek philosopher, had for the first time calculated the circumference of the earth and had devised lines of latitude and longitude to locate places on the earth
• Lines of Latitude


  Imaginary lines joining all places having the same latitude, towards north or south of the Equator
• Latitude


  The angular distance of a place north or south of the Equator
• Latitudes are calculated according to the angle a place makes with the centre of the earth
• Parallels of latitude are the lines of latitude that are parallel to the Equator and each other
• Only the Equator is a Great Circle, other parallels of latitude are full circles but not Great Circles
• The distance between each line of latitude is approximately 111 km
• Heat Zones


  • Lines of latitude divide the earth into distinct heat belts and climatic zones
• Heat Zones


  • Torrid or Tropical Zone (between Tropic of Cancer and Tropic of Capricorn)
  • Temperate Zones (between Arctic Circle and Tropic of Cancer, and between Antarctic Circle and Tropic of Capricorn)
  • Frigid Zones (between Arctic Circle and North Pole, and between Antarctic Circle and South Pole)
• Lines of Longitude


  Imaginary lines running north to south passing through the poles
• Longitude


  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°, passing through Greenwich near London
• There are a total of 360 lines of longitude at 1° interval
• All meridians of longitude converge at the poles and are thus of equal length
• The distance between two lines of longitude is maximum at the Equator (111 km) and decreases towards the poles
• Meridians of Longitude


  The lines of longitude, derived from the Latin word 'meridianum' meaning noon, as the sun crosses a meridian at noon
• Longitude


  Determines the local time of a place, with a difference of 4 minutes per 1° longitude
• The Earth makes a complete circle on its axis, covering 360° longitudes in 24 hours, or 1° longitude every 4 minutes
• The formula 'EGA-WLS' is used to remember that for each 1° longitude towards East, time is gained and added, while towards West, time is lost and subtracted
• The Prime Meridian (0°) and the 180° meridian together make a full circle round the earth
• Longitude


  Imaginary lines running east to west on a globe
• Latitude


  Imaginary lines running north to south on a globe
• Geographic Grid


  • Criss-crossing lines on a globe that form a framework
• Characteristics of lines of latitude


  • They are imaginary lines
  • They are parallel to the Equator
  • They reduce in length as we go towards the poles
• Characteristics of lines of longitude


  • They run parallel to the Prime Meridian
  • They are not parallel to each other
  • They converge at the poles
• Great Circle


  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, and whose centre is also the sphere's centre
• Characteristics of a Great Circle


  • It is a theoretical circle formed by the intersection of the earth's surface and an imaginary plane that passes through the centre of the earth and divides it into two equal parts
  • All such circles must pass through or touch the centre of the circle
  • Infinite number of circles that touch the two opposite ends of the sphere can be drawn on a sphere
  • Intersecting great circles always bisect each other
• Uses of Great Circles


  • Navigators use great circles to determine the shortest distance between any two points on the earth's surface
  • Great Circle routes are specially important for places that are on opposite sides of the globe
  • Great circles are used by meteorologists to determine climate and weather conditions in a region
• Small Circle


  Circles which do not pass through the centre of the earth
• Standard Time


  The uniform time based on a central meridian
• Greenwich Mean Time (GMT)


  The time at 0° longitude, used as the reference for time zones
• Indian Standard Time (IST)


  The time zone for India, which is 5.5 hours ahead of GMT
• Calculating time at a place


  1. Determine the longitude difference from the reference meridian

  2. Add or subtract the time difference based on the direction from the reference meridian
• International Date Line (IDL)


  The 180° line of longitude, where the date changes when crossing it
• The International Date Line bends and goes zig-zag at the Bering Strait between Siberia and Alaska and at Fiji, Tonga, New Zealand and some other Islands to avoid confusion of having different dates within the same country
• Locating places on a map or globe


  1. Identify the relevant latitude and longitude of the place

  2. The point where the latitude and longitude lines intersect is the location of the place
• Longitude


  The angular distance of a place east or west of the Prime Meridian, measured in degrees (0-180 degrees east or west).