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Welcome to the U. S. Geological Survey (USGS) Gap Analysis Program (GAP) web site. The USGS is committed to and is making every possible effort to ensure that all electronic and information technology developed, procured, maintained, or used by the USGS is accessible to people with disabilities, including both employees and the customers we serve.

Adobe Acrobat PDF Files

Many of the documents on the NTSB Web site are in HTML or ASCII (plain text) formats. These formats are generally accessible to people who use screen readers.  In addition, the NTSB also provides a large number of documents in Adobe Acrobat® Portable Document Format (PDF) on the NTSB Web site.

GAP utilizes PDF format to preserve the content and layout of our hard copy publications. Publications in PDF can only be viewed and printed using the Adobe AcrobatReader®, version 3.0 or higher.  You can download and get help using the Acrobat Reader at the Adobe Systems, Inc. site.  The downloadable Acrobat Reader software is available at NO CHARGE from Adobe, at

If you cannot fully access the information on a particular page, please email the contact person, or group, named in the footer information at the bottom of the page and they will help you. This may include providing the information to you in an alternate format.

For further information and to learn more about the regulations governing the accessibility of Federal electronic information products, visit the Section 508 pages listed below: