A RARE 18th century map of the early British colonies in America drawn up by a Caernarfonshire man is expected to sell for $50,000.

New York’s Swann Auction Galleries is selling one of the most important historical plans of the region on Thursday, June 6.

The 1755 chart was drawn up by surveyor Lewis Evans, from as A General Map of the Middle British Colonies in America.

It set the standard for map making in the area for the next 50 years.

Evans, who had already become a close friend of Benjamin Franklin, covered vast tracts of land in his map, showing Virginia, Maryland, Delaware, Pennsylvania, New Jersey, New York, Connecticut and Rhode Island, as well as Ohio and parts of what was to become Canada.

His descriptions of land beyond the British frontier into the Ohio territory included new information, offering potential settlers and speculators the most detailed and accurate look at land in the west.

What makes the map so rare, is that it is not the final published map but a working proof showing how Evans approached the task and the decisions he took.

“This is the maker of an 18th century American map literally signing off on the work-in-progress printing of his map which would go on to have historic implications 53 days before it was to be a finished product and ready to be officially published June 23, 1755,” said Swann Galleries’ specialist Caleb Kiffer.

“This is the kind of item one thinks to be impossible but has had the good fortune to surface and be appreciated by those who would appreciate it.”

Kiffer notes that the general cartography is laid down, but finishing touches are lacking, most notably Evans’ own engraved name, the engraver, Benjamin Turner’s name, cartouches and insets, tables, anecdotes and the publishing imprint.

“Virtually all the major place names and toponyms seen on the finished map are not engraved yet.

“Evans has written a few of these names in manuscript to be later engraved and has filled the distance tables at lower right in ink, correctly corresponding to the engraved version. Below the tables is an ink signature: ‘Lewis Evans ... May 2, 1755’.

“Rarely, if ever, has a piece of an 18th century map’s publication story been preserved or offered for sale.”

The map’s importance was strategic as well as geographic. Part-financed by Thomas Pownall, the secretary to the Governor of New York, the map was published in Evans’ Geographical Essays, the British authorities made extensive use of it during the French and Indian War (1754-63).

The map will appear in the Maps & Atlases, Natural History & Color Plate Books auction. The estimate is $30,000 to $50,000.

For information on the auction or to bid online see the website www.swanngalleries.com or for more information contact swanngalleries.com.