GPS provides many benefits to civilian users. It is vulnerable, however, to interference and other disruptions that can have harmful consequences. GPS users must ensure that adequate independent backup systems or procedures can be used when needed. Interagency GPS Executive Board. GPS Policy, Applications, Modernization, International Cooperation. February 2001.
Thomas, Michael L.
"Evolution of GPS Systems Architecture and Its Impacts,"
Communications of the IIMA: Vol. 10
, Article 3.
Available at: http://scholarworks.lib.csusb.edu/ciima/vol10/iss4/3