Bad maps are the whole reason for Delaware's existence.
Ownership of the west shore of Delaware Bay had been controversial because of the Swedish and Dutch settlements that had preceded the settlement of Maryland.
The preamble of the Charter of Maryland states that Lord Baltimore desired to set up
a numerous Colony of the English Nation, to a certain Region, herein after described, in a Country hitherto uncultivated, in the Parts of America.
and there would be much focus later on the word 'uncultivated' as a legal distinction. Since the (then) Swedish settlement wasn't a British colony, Lord Baltimore claimed ownership, but didn't have the resources to exercise the claim.
In 1665, Admiral Penn captured the area in question from the Dutch, and King Charles II granted Penn's son William an area north of the Fortieth Parallel plus a circle twelve miles from the former Swedish/Dutch settlement, now called New Castle. (Because the Fortieth Parallel is much more than twelve miles north of New Castle, this technically put Philadelphia within Maryland). Much hilarity ensued.
In 1685, King James II had set the boundary between Maryland and what was then called the "Three Lower Counties" as a line from the 40th Parallel to the midpoint of an east-west line between Cape Henlopen and the Chesapeake Bay, then east to Cape Henlopen.
On the last day of October the committee proposed in the presence of Baltimore and Penn, that the whole peninsula or tract of land called Delaware, as far as Cape Henlopen southward...be divided equally between His Majesty and Lord Baltimore.
"History of the Boundary Dispute Between the Baltimores and Penns Resulting in the Original Mason and Dixon Line" by Edward Bennett Matthews, Maryland Geological Survey, 1908, Volume 7.
One of the first things Parliament did after the Glorious Revolution, even before the English Bill of Rights, was to revoke the Charter of Maryland, and it took 26 years, conversion to Anglicanism, and a new king from Germany, who didn't speak much English, for the Calverts to get Maryland back. In the meantime, the Penns had been given the Three Lower Counties and their claims had widened.
In 1732, Lord Baltimore and the descendants of William Penn tried to use this map to resolve the boundary dispute between Maryland and Pennsylvania:
Source: Wikimedia Commons
This was a map commissioned by Lord Baltimore, but the cartographer had based it off a very inaccurate Dutch map from 1651.
Compare to the actual location of Cape Henlopen:
Lord Baltimore felt he had been tricked, and sued to get this submission changed, to no avail.
Had he referred to Augustine Herrman's map of 1673, or Christopher Browne's map of 1685, or Joan Vinckeboons's map of 1639, things might have been different.
Nevertheless a mini-war between Maryland and Pennsylvania ensued and it took George II and some proper surveyors to set the boundary straight. Nevertheless, minor disputes continued until 1908.