Final answer:
The Equator and the Prime Meridian are the most important reference lines on Earth, set at 0 degrees latitude and 0 degrees longitude respectively. They serve as the basis for the Earth's grid system used for navigation and geographical measurements.
Step-by-step explanation:
The two most important reference lines on the earth are the Equator and the Prime Meridian. The Equator is the longest line of latitude, and it is considered 0 degrees latitude. It divides the earth into the Northern and Southern Hemispheres. On the other hand, the Prime Meridian is the line of longitude that runs through the Royal Observatory in Greenwich, England, and is designated as 0 degrees longitude. This meridian divides the earth into the Eastern and Western Hemispheres. All lines of longitude are measured east or west from the Prime Meridian up to 180 degrees.
Lines of latitude and longitude form a grid pattern known as the graticule, which covers the entire globe. This grid allows for any absolute location on the Earth to be measured and described in terms of degrees north or south (latitude) and east or west (longitude), enabling precise navigation and geographical study.