CONCORD, N.H. — Experts have raised questions about the border map Gov. Jeanne Shaheen is using to show the Portsmouth Naval Shipyard is in New Hampshire, not Maine.

Shaheen brought back the 1761-era map from a trade mission to Britain two months ago and said it “clearly shows the shipyard” on Seavey Island is in New Hampshire.

Actually, the map also can be found at the state library across the street from the Statehouse.

Shaheen emphasized the yellow painted lines on the map highlighting Maine and Massachusetts. One outlines the southern portion of Maine on the east side of the river, which Shaheen said is proof the Piscataqua River and its islands belong to New Hampshire.

But librarian William Copeley of the New Hampshire Historical Society said that could be misleading.

“Generally, the coloring of maps was done for artistic reasons, just to make the map more beautiful,” he said. He said they are not meant to be boundaries.

Old mapmakers also wrote that the border between the states is in the middle of the Piscataqua River, which places Seavey Island on the Maine side.

Other experts consider whoever possesses a thing has a right to it, and land access to the shipyard is in Maine.

But Doug Hattaway, Shaheen’s press secretary, said the map will be used to back New Hampshire’s claim to the shipyard.

All shipyard workers must pay income tax to Maine. The shipyard has about 3,300 workers, and close to half live in New Hampshire, and they pay Maine about $3 million in taxes each year.