The eastern half of Martha’s Vineyard is called Down-Island and the western half is called Up-Island. Why you ask? To confuse you, that’s why. Not really, at least not on purpose. There is a very logical reason and here it is according to the MV website.
” Up-Island is the western area, which comprises the three rural towns of Aquinnah, Chilmark and West Tisbury. Down-Island is the eastern portion, home to the larger historic villages of Edgartown, Oak Bluffs and Vineyard Haven (also known as Tisbury). The two terms come from the rich seagoing tradition of Martha’s Vineyard, which once sent its whaling ships circuling the globe heading “up” in nautical terms takes you “west” because it’s further from zero degrees of longitude in Greenwich, England, home of the Prime Meridian.”
Well then, according to the Guide to Martha’s Vineyard we have this explanation. “When a ship sails in an easterly direction, it is decreasing or running “down” the degrees of longitude toward zero at Greenwich, England. A westbound vessel, on the other hand, is running “up” its longitude. Thus the Down-Island town are those on the eastern and northeastern end of the Island. The Up-Island communities are at the western end. A ship moving through Vineyard Sound sails “up” to New York and “down” east to Maine.” Ah ha.
OK, I’m still confused but I do know how to get from Down-Island to Up-Island and not get lost… it’s an Island, how lost could one get anyway.
Got all that… me neither 
But that’s not the only confusion about the Vineyard … she had an identity crisis at one time involving Massachusetts and New York.
Martha! Martin! New York! Massachusetts! How many aliases and states have claimed this 100 sq mile island? The Wampanoags named it Noepe and that stuck until Bartholomew Gosnold came along in 1602.
No one seems to know who the Martin was whose name was once attached to the Vineyard… so let’s move ahead to Martha whose identity is still shrouded in myth. Was she one of Gosnold’s daughters, or his mother, or the name of an English royal. Whoever she was her name stuck and in my opinion has a nicer ring to it then Martin’s Vineyard.
According to the book “The History of Martha’s Vineyard” by Arthur R. Railton, in 1664 Charles II gave NY, NJ and the islands to the east to his brother, the Duke of York. In 1670 Thomas Mayhew, Jr and his grandson Matthew of Massachusetts traveled to NY to ask Gov Lovelace which colony his Island was under… New York or Massachusetts. Gov Lovelace made Thomas Mayhew “Governor for Life” of Martha’s Vineyard and gave him the authority to collect rents from all who lived within its bounds. Voila, Martha’s Vineyard Massachusetts. History lesson over.
