Meridian (geography)
From Tardis Wiki, the free Doctor Who reference
According to a book owned by Chloe Webber, meridians or lines of longitude were imaginary lines on the globe of the planet Earth which ran at right angles to the parallels or lines of latitude.
The prime meridian (0 degrees longitude) ran through Greenwich in London. Other lines of longitude were measured 180 degrees east and 180 degrees west of the prime meridian. On the opposite side of the world from the prime meridian, around 180 degrees east or west, lay the International Date Line. (TV: Fear Her [+]Loading...["Fear Her (TV story)"])
