Geographic Grid Latitudes and Longitudes Chapter Notes | Geography for SSS 1 PDF Download

Introduction

Latitude and Longitude

• The Geographic Grid is a network of latitude and longitude lines drawn on a globe or map to locate places.
• The Equator and Prime Meridian are the main reference lines for this grid.
• The Equator is an imaginary horizontal line at 0° that splits the Earth into the Northern and Southern Hemispheres.
• Latitude measures how far a point is north or south of the Equator, in degrees, from the Earth's center.
  • Lines of latitude connect places with the same latitude and are called parallels because they run parallel to the Equator, from west to east.
  • The Equator, at 0°, is the longest latitude line; other parallels get shorter as they move toward the poles, which are just points at 90° N and 90° S.
  • Only the Equator is a great circle among latitude lines; others are smaller circles.
  • There are 181 latitude lines (90 north + 1 Equator + 90 south), spaced 1° apart.
  • The distance between two consecutive latitude lines is about 111 km (69 miles).
• Latitude lines help in:
  • Calculating ground distances between places north or south of the Equator.
  • Identifying the Earth's thermal zones.
  • Locating places when combined with longitude lines.
• Key latitude lines include:
  • Equator (0°)
  • Tropic of Cancer (23½° N)
  • Tropic of Capricorn (23½° S)
  • Arctic Circle (66½° N)
  • Antarctic Circle (66½° S)
  • North Pole (90° N)
  • South Pole (90° S)
• Thermal zones based on latitude:
  • Torrid Zone: Between Tropic of Cancer (23½° N) and Tropic of Capricorn (23½° S); the hottest zone.
  • Temperate Zone: North Temperate Zone (23½° N to 66½° N) and South Temperate Zone (23½° S to 66½° S); moderate temperatures.
  • Frigid Zone: North Frigid Zone (66½° N to 90° N) and South Frigid Zone (66½° S to 90° S); very cold temperatures.
• Longitude measures how far a point is east or west of the Prime Meridian, in degrees, from the Earth's center.
• Lines of longitude, or meridians, connect places with the same longitude, running from pole to pole.
• Meridians are called so because places along the same meridian experience noon at the same time.
• All meridians are equal in length, forming semicircles that meet at the poles.
• Opposite meridians (e.g., 180° E and 180° W, or 0° and 180°) form great circles.
• There are 360 meridians (180 east + 180 west), spaced 1° apart.
• The distance between two consecutive meridians is 111 km at the Equator but decreases toward the poles, where it becomes 0.
• Longitude helps in:
  • Locating places on a globe or map by plotting meridians from pole to pole.
  • Determining time differences between places.
    
• Longitude and time relationship:
  • The Earth rotates 360° in 24 hours, covering 15° per hour or 1° every 4 minutes.
  • When it’s noon at the Prime Meridian (0°), places east of it are ahead in time, and places west are behind.
  • For every 1° east, add 4 minutes; for every 1° west, subtract 4 minutes to find local time.
• Great circles:
  • A great circle is any circle that passes through the Earth’s center, dividing it into two equal halves.
  • All meridians paired with their opposite meridians (e.g., 0° and 180°) form great circles.
  • The Equator is the only latitude line that is a great circle.
  • Great circles are used to find the shortest routes for ships and aircraft, saving time.

Concepts of Longitudes - Prime Meridian, GMT & IDL

• Longitudes are used to calculate the time at different places.
• The Earth’s rotation causes variations in sunrise and sunset times across places.
• The Earth rotates 360° in 24 hours, covering 15° of longitude per hour or 1° every 4 minutes.
• If it’s 12 noon at the Prime Meridian (0°), it’s 1 p.m. at 15° E and 11 a.m. at 15° W, as the Earth rotates west to east.
• Local time is based on the Sun’s position overhead at noon at a specific place.
• Local time changes by 4 minutes for every 1° of longitude.
• Standard time is the uniform time used across a country, based on the local time of its central meridian (Standard Meridian).
• Greenwich Mean Time (GMT) is the standard time at 0° longitude, used in Great Britain.
• A time zone is a region using the same standard time, typically covering 15° of longitude.
• The world is divided into 24 time zones, each spanning 15° of longitude.
• The International Date Line(IDL) is an imaginary line near 180° E/W in the Pacific Ocean, adjusted to avoid landmasses for consistent time and date.
  • Crossing the IDL from east to west adds a day; crossing from west to east subtracts a day.
  • The Prime Meridian (0°) and IDL (180°) divide the Earth into Eastern and Western Hemispheres.
  • Some geographers use 20° W and 160° E as the boundaries for the Eastern and Western Hemispheres.
• Great circles:
  • A great circle is a circle that passes through the Earth’s center, splitting it into two equal parts.
  • The Equator and all pairs of opposite meridians (e.g., 0° and 180°) are great circles.
  • Great circles are the largest circles on a sphere, used for navigation to find the shortest routes.
  • The Equator is the only east-west great circle.
  • Great circle distance formula: d = r cos^-1[cos σ₁ cos σ₂ cos(Λ₁ - Λ₂) + sin σ₁ sin σ₂]

Key Words

• Geographic Grid: A system of latitude and longitude lines on a globe to locate places.
• Latitude: The angle measuring a point’s distance north or south of the Equator, in degrees.
• Longitude: The angle measuring a point’s distance east or west of the Prime Meridian, in degrees.
• Meridians: Vertical lines connecting places with the same longitude, running from pole to pole.
• Prime Meridian: The 0° longitude line, passing through Greenwich, used as a reference for east-west measurements.
• Local Time: Time based on the Sun’s position overhead at noon at a specific place.
• Standard Time: Uniform time across a country, based on its central meridian’s local time.
• Time Zone: A region using the same standard time, covering about 15° of longitude.
• IDL: The International Date Line, near 180° longitude, where crossing changes the date.