A C172 SINGLE PLT VIOLATED THE DC ADIZ ENRTE TO ANP.

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I DEPARTED BRANDYWINE (N99) FOR OCEAN CITY; MD (OXB) VFR AND ARRIVED WITHOUT INCIDENT. AFTER A 2 1/2 HR STOP-OVER; DEPARTED OXB FOR LEE ARPT (ANP; ANNAPOLIS; MD). FLEW N TO ATR VOR; THEN OUTBOUND ON THE 290 DEG RADIAL TO ANP. NO FLT PLAN WAS FILED. ON LNDG AT LEE; I WAS MET BY UNITED STATES CUSTOMS OFFICERS. THEY INFORMED ME THAT ON XING THE CHESAPEAKE BAY; I HAD ENTERED THE WASHINGTON; DC ADIZ WITHOUT CLRNC OR A DISCRETE XPONDER CODE. PRIOR TO DEPARTING N99; I RECEIVED A WX BRIEFING FOR MY FLT; INCLUDING LNDG AT ANP. I DID REVIEW THE NOTAMS REGARDING WASHINGTON DC; BUT THEY ARE VERY CONFUSING. REFERRING TO BOTH THE WASHINGTON SECTIONAL AND TERMINAL; THEY CLRLY DEPICT THE SPECIAL FLT RULES AREA (SFAR 94). I MISTOOK THIS FOR THE DC ADIZ. HAD I RECEIVED A VERBAL BRIEFING; AS OPPOSED TO A COMPUTERIZED BRIEFING; AND FILED A FLT PLAN; I ASSUME FSS WOULD HAVE ADVISED ME OF THE NEED FOR AN ADIZ FLT PLAN AND THE NEED TO CONTACT POTOMAC APCH FOR A XPONDER CODE. THE MAJOR PROB; I FEEL; IS THE FAA FAILURE TO CLRLY DEPICT THE LOCATION OF THE ADIZ AND INCLUDE WARNINGS OF THE DANGERS ASSOCIATED WITH IT ON ALL CHARTS; JUST AS THEY DO WITH PROHIBITED AND RESTR AREAS.