Practical Work in Geography

Latitude, Longitude and Time

The Earth is nearly spherical but not a perfect sphere. Its equatorial radius is larger than its polar radius due to the Earth's rotation causing a bulge at the equator, making its shape an oblate spheroid. This shape presents challenges in accurately positioning surface features because there is no fixed reference point on the surface. To overcome this, a network of imaginary lines is drawn on globes and maps to locate places precisely. These lines form the geographical grid, consisting of two sets of lines: parallels of latitude and meridians of longitude. The Earth spins on its axis from west to east, creating two natural reference points: the North Pole and the South Pole. These poles form the basis of the geographical grid. The horizontal lines, called parallels of latitude, run east-west and are parallel to each other. The equator is the most important parallel, drawn midway between the poles, and divides the Earth into the Northern and Southern Hemispheres. It is the largest circle on the globe and is called a great circle. Other parallels are smaller circles (small circles) that decrease in size as they move towards the poles. Vertical lines running north-south are called meridians of longitude. They join the two poles and are widest apart at the equator, converging at the poles. Together, these lines provide a coordinate system that helps in determining the location, distance, and direction of places on Earth. Latitude and longitude are measured in degrees (°), with each degree subdivided into 60 minutes (′) and each minute into 60 seconds (″).

• Earth's shape is an oblate spheroid due to equatorial bulging caused by rotation.
• Geographical grid consists of parallels of latitude (horizontal) and meridians of longitude (vertical).
• Equator is the 0° latitude line and divides Earth into Northern and Southern Hemispheres.
• Parallels of latitude are circles parallel to the equator; meridians of longitude are semicircles joining poles.
• Latitude and longitude are angular measurements in degrees, minutes, and seconds.
• Coordinates help locate places, measure distances, and determine directions.
• 📌 Oblate spheroid: The shape of the Earth, flattened at the poles and bulging at the equator.
• 📌 Parallels of latitude: Imaginary horizontal lines parallel to the equator measuring angular distance north or south.
• 📌 Meridians of longitude: Imaginary vertical lines joining the poles measuring angular distance east or west.

60 Parallels of Latitudes

Latitude of a place is defined as its angular distance north or south of the equator, measured along the meridian of that place from the Earth's center. Lines joining places of the same latitude are called parallels. The equator is at 0°, while the poles are at 90°N and 90°S respectively. If parallels are drawn at one-degree intervals, there will be 89 parallels in both the Northern and Southern Hemispheres, totaling 179 including the equator. Each parallel is smaller than the equator, except the equator itself which is the largest great circle. The latitude is always expressed with a letter N or S to indicate the hemisphere. If the Earth were a perfect sphere, the length of one degree of latitude would be constant at approximately 111 km everywhere. However, due to the Earth's oblateness, this length varies slightly from about 110.6 km at the equator to 111.7 km at the poles. Latitude can be determined using the altitude of the sun or the Pole Star. This measurement is crucial for navigation and mapping. The chapter also explains how to draw parallels of latitude on paper using a circle and a protractor. By dividing a circle with a horizontal line representing the equator and marking angles from it, parallels such as 20°S can be drawn as lines parallel to the equator.

• Latitude is angular distance north or south of the equator measured along meridians.
• There are 179 parallels including the equator, spaced at one-degree intervals.
• Equator is 0°, poles are at 90°N and 90°S.
• Length of one degree latitude varies slightly from 110.6 km at equator to 111.7 km at poles.
• Latitude is determined using celestial observations like the sun or Pole Star.
• Parallels can be drawn on paper using a circle and protractor to mark angles from the equator.
• 📌 Latitude: Angular distance north or south of the equator.
• 📌 Parallels: Lines joining points of equal latitude.
• 📌 Great circle: The largest circle on the globe, e.g., the equator.