HDG TRACK POS DEV IN A NON ADHERENCE TO ATC CLRNC INSTRUCTION.

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MIA DEP CTL WAS GIVING US RADAR VECTORS FOR TFC SEPARATION AND WX AVOIDANCE TO JOIN ENRTE RTE STRUCTURE WITH ZMA. OUR FILED ROUTING AND CLRNC WAS MIA DIRECT ORL ENRTE (MIA5 SID). WE REQUESTED DEVS AROUND NUMEROUS BUILDING CELLS AND THEN ACCEPTED CLRNC FROM DEP CTL TO 'FLY HDG 300 DEGS; JOIN J-53.' OUR POS WAS NEARBY (APPROX 10 NM N) OF MIA VORTAC; AND THIS HDG SEEMED PLAUSIBLE AND REASONABLE. DEP CTL THEN HANDED US OFF TO ZMA ARTCC. I HAD UNEASY FEELING AFTER ABOUT 1 MIN OF FLYING THE ASSIGNED 300 DEG HDG BECAUSE WE REALLY HAD NO COURSE GUIDANCE (ORL VORTAC AT OUR RANGE AND ALT WAS UNRECEIVABLE) AND I TRIED TO VISUALIZE POS RELATIVE TO MIA VORTAC. RIGHT AFTER RADIO HDOF TO CTR I INSTRUCTED FO (PNF) TO PROGRAM COORDINATES FOR DOUGS INTXN (BEGINNING OF J-53) AND I GENERATED J-53 EXTENDED CTRLINE ON THE OMEGA AND SAW WE WERE 7.5 NM L OF CTRLINE. EXECUTED TIGHT R TURN TO INTERCEPT EXTENDED CTRLINE; ALTHOUGH AT OUR POS THE AIRWAY DID NOT EXIST. FO CHKED IN WITH CTR AND HE ADVISED WE WERE W. WE HAD FLOWN PREVIOUS INSTRUCTIONS AND THEY DID NOT COMPLY WITH DEP'S AND CTR'S EXPECTATIONS. WHAT DEP MEANT AND EXPECTED BUT DID NOT ASSIGN WAS 'FLY HDG 300 DEGS TO INTERCEPT ORL 160 DEG RADIAL.' I ASSUME HE MENTALLY WAS EXPECTING INTERCEPT OF WHAT USED TO BE J- 53 BUT NO LONGER EXISTS. PERHAPS HIS VIDEO MAP IS NOT CORRECTED OR BY FORCE OF HABIT HE PICTURED THE AIRWAY. HAD THERE NOT BEEN TSTMS OR HAD I BEEN FLYING WITH MORE SITUATIONALLY AWARE COPLT; WE COULD HAVE HAD OMEGA RNAV IMMEDIATELY AWAITING SUCH AMENDED CLRNC. HAD I BEEN PNF I WOULD HAVE HAD OMEGA ALREADY SET UP. NEXT TIME;; ANTICIPATE EVERYTHING; ASSUME NOTHING; CLARIFY EVERYTHING.