McGrath, each of the 50 states has a two letter capitalized code that is used in all postal mail and shipping addresses. Most Americans know that LA is Louisiana just as CA is California, AZ is Arizona, PA is Pennsylvania, etc. We still refer to Los Angeles as L.A., though. The states that get people confused are the least populated ones like mine, MT (Montana). When I order something over the phone and I'm giving my address sometimes the abbreviation for MT is confused with Minnesota, MN. Sometimes Mississippi, MS, is confused with Missouri, MO, Alaska, AK, with Arkansas, AR, with Arizona, AZ. But, that is how the post office has functioned in moving mail for decades.
We often call Washington, The District of Columbia, just "DC". The state of Washington, WA, is on the opposite side of the continent.

US State Abbreviations:
http://www.usps.com/ncsc/lookups/usps_abbreviations.html
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