Locality Rule Vs. National Standard Rule for Physicians

Define what is normally referred to as the “national standards rule” and “the locality rule” in describing the norms and expectations of appropriate medical care in the United States. In what instances, if any, should the locality rule prevail over the national standards rule? Further, is it practicable to have a national standards rule over the locality rule in the real world where the amount and kind of real resources does vary from one locale to another? Why is the national standard becoming more prevalent?
Should these rules (either or both) apply to non-physicians as well as physicians?