The data is Public Domain, with only the following conditions imposed:

"As an agency of the United States government, NIMA makes no copyright claim under Title 17
 of the United States Code with respect to any copyrightable material compiled in these products,
 nor requires compensation for their use."

"When incorporating the NIMA maps into your product, please include the following:

a.  "this product was developed using materials from the United States National Imagery and
 Mapping Agency and are reproduced with permission",
b.  "this product has neither been endorsed nor authorized by the United States National Imagery
 and Mapping Agency or the United States Department of Defense"."

"With respect to any advertising, promoting or publicizing of this product, NIMA requires that
 you refrain from using the agency's name, seal, or initials."