C182 MISUNDERSTOOD ATC CLRNC AND FOLLOWED THE SHORELINE THROUGH THE LAX TCA RATHER THAN FOLLOW THE SHORELINE RTE DEPICTED ON THE CHART. FURTHER; RPTR GIVES NO INDICATION HE WAS AWARE OF ANY ALT ASSIGNMENT.

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PRIOR TO DEP WE CALLED SANTA MONICA GND AND SAID WE WOULD LIKE TO GO S OVER LAX. HE GAVE US INSTRUCTIONS THROUGH THE VFR CORRIDOR. AFTER OUR RUN-UP WE CALLED SMO TWR AND SAID WE WERE READY TO GO; SHE GAVE US INSTRUCTIONS THAT SEEMED TO BE CLRER AT THE TIME. OUR INSTRUCTION WAS TO FLY TO THE 'SHORELINE' AND DO A R 280 DEG TURN; ETC. WE INTERPRETED HER INSTRUCTIONS TO MEAN WE WERE TO FOLLOW THE SHORELINE S PAST LAX. WHILE IN THE 280 DEG TURN WE ASKED SMO TWR FOR A FREQ CHANGE TO APCH. SHE SAID TO STAY WITH HER THAT IT WOULD BE BETTER. SO WE STAYED ON SMO TWR FREQ UNTIL S OF HAWTHORN. THEN ASKED FOR A FREQ CHANGE AGAIN. GRANTED. WE CONTACTED SOCAL APCH AND WERE TOLD OF A POSSIBLE 'AIRSPACE VIOLATION.' UPON REACHING SAN DIEGO WE CALLED THE CTLR AND WERE TOLD WE WERE 200 FT TOO LOW AND TOO FAR W. MY OPINION: THE CTLRS AT SMO NEED TO BE CLEARER WITH THEIR DEP INSTRUCTIONS; ESPECIALLY WITH PEOPLE WHO MAY NOT BE FAMILIAR WITH THE AIRSPACE. THE CLRNC SHOULD SOUND THE SAME WHETHER FROM GND OR TWR. SINCE TWR ASKED US TO STAY WITH HER; WHY DID SHE NOT SAY WE WERE APCHING OR IN THE WRONG AIRSPACE. WE SHOULD HAVE NOT ACCEPTED AND DEPARTED WITH INSTRUCTIONS THAT WE WERE NOT 100% SURE OF. WE SHOULD HAVE STUDIED OUR CHARTS BETTER.