From where do lines of longitude extend?

Lines of longitude, also known as meridians, extend from the North Pole to the South Pole. They are used to determine positions east or west of the Prime Meridian, which is designated at 0 degrees longitude. Each line of longitude represents a half of a great circle that runs vertically around the Earth, connecting the two poles.

This format is essential for understanding Earth's geography because it allows for precise navigation and mapping. Lines of longitude are critical for global positioning, and they help in expressing time zones, as each time zone corresponds roughly to 15 degrees of longitude.

The other options do not accurately describe the nature of lines of longitude. The equator serves as a reference line for latitude, while lines of longitude specifically relate to the vertical measurements from pole to pole. Describing them as extending from "east to west" or referencing the atmosphere does not capture the correct geographical definition and concept of meridians.