Which description best fits meridians in geography?

Meridians in geography are defined as lines that run north to south. They are used for detailing the longitude of a location and help in navigation and mapping the Earth. Meridians are crucial in understanding the coordinate system used in cartography and in global positioning systems. They help to determine how far east or west a point is from the Prime Meridian, which is established at 0 degrees longitude in Greenwich, England.

The other descriptions do not accurately reflect the definition of meridians. Lines that run east to west are known as parallels or lines of latitude, which relate to measuring the distance north or south of the Equator. Lines that mark elevation points relate to topographic features such as contour lines or elevation markers, not meridians. Lastly, while time zones may be based on meridians, the lines themselves do not indicate time zones directly; rather, they help establish which time zone a particular meridian corresponds to, designed in reference to the Earth's rotation.