The network of imaginary lines formed by the latitudes and longitudes (that are perpendicular or orthogonal to each other) is called a grid.

The seasons are opposite in the two hemispheres. Thus, when the northern hemisphere has winter, the southern hemisphere experiences summer and vice versa.

The earth's axis is at an inclination of 23 1/2^o to the vertical.

Latitudes are circles of different diameters with the equator being the largest and those near the poles being the smallest.

Longitudes are measured in degrees from 0^o to 180^o, east or west of the Prime Meridian. The two important lines of longitude are the Prime Meridian (0^o) and the International Date Line (180^o.

Latitudes are parallel to each other and therefore never meet. Longitudes meet at the poles.

The Tropic of Cancer is in the northern hemisphere and the Tropic of Capricorn is in the southern hemisphere.

The Tropic of Capricorn is in the southern hemisphere and the Tropic of Cancer is in the northern hemisphere.

The Arctic Circle is near the north pole and the Antarctic Circle is near the south pole.

The Antarctic Circle is near the south pole and the Arctic Circle is near the north pole.

Longitudes meet at the poles and are widest apart at the equator. Thus, the distance between two longitudes does not remain constant. On the other hand, the distance between two latitudes remains the same.

Latitudes are circles of different diameters, with the equator being the largest and those near the poles being the smallest. Longitudes are semi-circles of equal size because they all extend from the north pole to the south pole.

Antarctica is also entirely south of the equator, but is an uninhabited continent. Much of Australia lies between 10^oS and 40^o. Australia being in the southern hemisphere will have winter when a country (e.g., India) in the northern hemisphere has summer and vice versa.

The equator crosses this South American country, and Ecuador is Spanish for equator.

Each rotation of the earth takes 24 hours (24 x 60 = 1440 minutes) and corresponds to 360^o in terms of longitudes. So, the velocity of the earth's rotation is 15^o in one hour. Thus, one degree of longitude corresponds to a time difference of 4 minutes (i.e., 1440 / 360).

Greenwich is the London borough that has given its name to the Prime Meridian (0^o) of the world. The Prime Meridian is also called the Meridian of Greenwich. The word "meridian" means "midday": lines of longitude are called meridians of longitude because places on the same longitude have "midday" at the same time. The International Date Line approximately follows the longitude of 180^o so as not to cross any land.