The equator divides the globe into two hemispheres of the North (N) and South (S). And is the beginer of latitude

Small circle - the circle formed on the surface plane of the section that does not pass through the center of the Earth,

Parallels are called small circles parallel to the equator.

It numbered from 0° to 90°, in the northern hemisphere - the northern latitude, and also from -0° to -90° in the southern hemisphere - the southern latitude. All the points lie on the same parallel have the same latitude.

What has geometric shape a cross-sectional plane of the equator, the parallels?

Meridians (large circle) - the line section of the surface of the Earth by a plane passing through the poles, they are called true or geographic meridians.

All points on the same meridian have the same longitude.

Meridian passing through astronomical observatory of Greenwich (near London), adopted by international agreement as the start and called Greenwich meridian (initial) and has a value of 0º longitude. Longitude reckoned eastward from the support - Greenwich to 180 ° is called the East and in the West to 180 ° - Western.

The prime meridian (Greenwich) divides the globe into two hemispheres Eastern (E) and West (W)

What are geometric shape cross-sectional plane of the meridian, and why?

Parallels and meridians form a grid coordinate depending on which figure it is located, formed geodetic, or spherical celestial coordinates.