The National Imagery and Mapping Agency blocked access to a wide range of its publicly available maps last week while officials reviewed the maps to make sure they did not contain information that could jeopardize national security.

NIMA issued the unprecedented freeze last Wednesday as a security precaution in the wake of the Sept. 11 terrorist strikes on the World Trade Center and the Pentagon, according to NIMA spokeswoman Joan Mears.

Last week, NIMA directed the U.S. Geological Survey and the Federal Aviation Administration to halt sales of all NIMA-made topographic maps and ordered the Library of Congress and National Archives and Records Administration to deny public access to such maps, Mears said. The sales restriction extended to private firms that are licensed to sell NIMA products. NIMA’s nautical and aeronautical maps, which are used for ship and air navigation, were not part of the review and are still available to the public, according to Mears.

The Library of Congress quickly obtained a waiver to the NIMA freeze so it could continue providing access to topographic maps of Vietnam, a popular collectors’ item among Vietnam veterans, according to Library officials and Ken Lee, CEO of Eastview Cartographic, a private firm that sells some NIMA products.

One intelligence expert questioned the wisdom of the freeze, noting that since NIMA is not the only source of map information, restricting access to NIMA maps will not improve security.