Newly Discovered Map of New York in Late 1776?

Earlier this month DNA Info New York reported that British map dealer Andrew Adamson says he might have found an unusual hand-drawn map of New York from 1776. The story goes:

A few years ago, Adamson was looking through archives at the United Kingdom Hydrographic Office in Somerset, England, when he came across a “very brown and dusty plan” that showed New York City and its surrounding areas.

“What was of immediate interest was the inclusion on the map of British troop positions, including General [William] Howe’s headquarters at Newtown, Long Island,” Adamson told DNAinfo New York via email. [The label “Head Quarters” seems to appear near the center of the detail above.]

Based on those troop positions, Adamson surmised that the map showed British-occupied New York in the summer of 1776, the period between the Battle of Brooklyn and the Battle of Harlem Heights. Adamson said he believes the document was part of a working military field map at the time.

Also of interest to Adamson was a second, smaller piece of paper at the center of the map that shows Manhattan in great detail. He said he believes this sheet is a drawing by Bernard Ratzer — a famous cartographer of that period — that was copied and used to make a larger, well-known Ratzer map of New York that was published in 1776. . . .

The rest of the map Adamson found was less carefully drawn, and he believes the smaller piece of paper was used as a starting point for other surveyors to sketch out the rest of it. He also believes the document is one portion of what was once a much larger map, since its edges are frayed.

The hand-drawn map, which belongs to a branch of the British government, still has to be authenticated.

Adamson’s firm, Heritage Charts, sells reproductions of the Ratzer map. A couple of years ago the Brooklyn Historical Society had its copy of that map conserved, and Barnet Schechter, author of The Battle for New York and George Washington’s America, spoke about it; that lecture is available as a podcast.