PLT OF C172; LACKING ADIZ CLRNC OR CODE; ENTERED DC ADIZ IN THE SOUTHERN PORTION WHICH IS NOT COINCIDENT WITH THE LATERAL EXTENT OF THE CLASS B AIRSPACE.

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THE FLT DEPARTED HUMMEL (W75) APPROX XA30 UNDER VMC. WE DECIDED TO RETURN TO HEF BY NAVING UP THE POTOMAC RIVER; WITH THE INTENT OF CONTACTING POTOMAC APCH FOR CLRNC INTO THE ADIZ AS WE APCHED THE BROOKE VOR (BRV). DURING THE ENTIRE RETURN TRIP WE WERE MONITORING THE EMER 'GUARD' FREQ AS REQUESTED OF ALL VFR FLTS. WE HEARD NO WARNINGS TO ANY ACFT ABOUT PENDING AIRSPACE VIOLATIONS. AT APPROX XB00; WE RADIOED POTOMAC APCH; GAVE OUR LOCATION AS 8 MI NE OF BRV; AND REQUESTED A SQUAWK CODE AND CLRNC INTO THE ADIZ TO HEF. HE GAVE ME A CODE AND ASKED ME TO IDENT. THE CTLR THEN SAID I SHOULD HAVE CONTACTED THEM SOONER; AND THAT I WAS ALREADY 5 MI INTO THE ADIZ. I EXPRESSED SURPRISE; SAYING I WAS STILL WELL S OF QUANTICO (NYG) AND THE CLASS B AIRSPACE. HE INDICATED THE ADIZ EXTENDED S OF THE CLASS B AIRSPACE IN THAT AREA. I ASKED IF I SHOULD EXIT THE AIRSPACE; BUT HE TOLD ME TO PROCEED TO MY DEST AND GAVE ME A PHONE NUMBER TO CALL UPON MY ARR. THE FLT TERMINATED AT APPROX XB15 AT HEF; AND I CONTACTED THE POTOMAC TRACON BY PHONE. I HAD A LENGTHY DISCUSSION WITH THE CTLR ABOUT THE DIMENSIONS AND BOUNDARIES OF THE ADIZ; AND HE INFORMED ME THAT I HAD ACTUALLY ENTERED THE ADIZ NEAR (NDY); EXITED IT AS I PROCEEDED W ALONG THE RIVER'S COURSE; THEN RE-ENTERED IT AS I TURNED N TOWARD HEF. HE INDICATED THAT HE WAS REQUIRED TO FILE A RPT ON THE INCIDENT; AND THAT THE FLT STANDARDS OFFICE OF THE FAA WOULD CONTACT ME. THIS INCIDENT OCCURRED AS A RESULT OF MY NOT BEING FAMILIAR WITH THE CONFIGN OF THE ADIZ IN THIS AREA. ALL OF MY PERVIOUS FLTS SINCE THE ADIZ WAS INSTITUTED DEPARTED TO OR ARRIVED FROM THE SW; W; NW OR NE. IN FACT; THROUGHOUT THE AREA OF MY INCURSION; THE ADIZ IS NOT COINCIDENT WITH THE CLASS B AIRSPACE; AND DUE TO ITS 'TEMPORARY' NATURE; IT IS NOT INCLUDED ON ANY CHARTS OR IN ANY NAV SYS. I FULLY UNDERSTAND MY RESPONSIBILITY TO BE FULLY INFORMED ABOUT ALL ASPECTS OF THE FLT I WAS UNDERTAKING; BUT I BELIEVE THAT THE CONFUSING CONFIGN OF THE ADIZ; PARTICULARLY NOT BEING COINCIDENT WITH ANY AIRSPACE THAT CAN BE IDENTED ON A PUBLISHED CHART; WAS A CONTRIBUTING FACTOR. IN THE FUTURE I WILL ENSURE THAT I AM MORE COMPLETELY BRIEFED PRIOR TO MY DEP.