Meridians of Longitude
Illustration showing how longitude lines cut the globe in planes that intersect at the polar axis. Longitude is a measurement that identifies a location as being a certain distance east or west of a prime meridian. Penobscot Marine Museum is located 68 degrees 55 minutes west of the Prime Meridian which passes through Greenwich, England.
This illustration is from Bowditch's American Practical Navigator, H.O. Pub. No. 9, 1975, p. 444.