TXWY INCURSION WHEN A B767 PIC FAILS TO HOLD SHORT OF TXWY B WHEN HE BELIEVES THAT HE IS STILL ON THE COMPANY RAMP AREA AT LAX; CA.

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DURING TAXI OUT OF ALLEY AT LAX; WE INADVERTENTLY CROSSED THE RAMP HOLD LINE WITHOUT TALKING TO ATC AND WERE HOLDING SHORT OF TXWY B. WE WERE MONITORING THE GND CTLR'S FREQ AFTER BEING PASSED OFF BY METERING. THERE WERE A LOT OF ITEMS GOING ON AT THE TIME WITH THE NORMAL RADIO TFC FOR PUSHBACK/TAXI PLUS I WAS CONCERNED ABOUT WHETHER WE WERE TAXIING IN ALLEY X OR ALLEY Y. AS WE APCHED THE END OF THE ALLEY; THERE WAS AN AIRPLANE WAITING TO ENTER THE ALLEY ON OUR R AND CONSTRUCTION TO OUR L WHERE TXWY ENDED. WE APPARENTLY PASSED THE RAMP HOLD LINE WITHOUT SEEING IT. A REVIEW OF THE ARPT CHARTS DOESN'T REVEAL WHERE THE LINE BTWN RAMP AND TXWY IS. WITH NO TXWY ON OUR L AND COMPANY ACFT ON OUR R WAITING TO ENTER THE ALLEY; WE THOUGHT WE WERE STILL HOLDING ON THE COMPANY RAMP. WHILE WE WERE HOLDING SHORT OF TXWY B; ATC CALLED AND TOLD US WE WERE ON THE TXWY ALREADY. WE RESPONDED THAT WE THOUGHT WE WERE ON THE RAMP; BUT THEN DISCOVERED WE WERE ALREADY ON TXWY X. FACTORS INVOLVED ARE TASK SATURATION; UNFAMILIARITY WITH THE ARPT AND CONFUSION OVER WHICH ALLEY OUR ACFT WAS PARKED IN. ADDITIONALLY; I DID NOT HAVE A CLR IDEA OF WHERE THE RAMP ENDED AND TXWY BEGAN. THAT ENTIRE AREA IS CONCRETE AND NOT READILY DISCERNIBLE AS TO TXWY DELINEATIONS.