LGT MADE TRANSITION FROM OUTER TAXIWAY TO INNER TAXIWAY AT 'Q' INSTEAD OF AT 'C' AS CLRED.

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GND HAD INSTRUCTED OUR FLT TO CROSS RWY 15R AND TAXI TO GATE VIA 'THE OUTER; CHARLIE; TO THE GATE.' THERE WAS NO MENTION MADE OF ADDITIONAL TAXIING ACFT IN OUR VICINITY. AS WE APCHED GATE ON THE OUTER; WE MADE A R TURN ONTO THE INNER RAMP AT WHAT WE THOUGHT WAS TAXIWAY C. AFTER HAVING REFERRED TO THE AIRFIELD DIAGRAM IN OUR MANUAL. GND INFORMED US WE HAD TURNED ON TAXIWAY QUEBEC. THERE WAS NO CONFLICT WITH GND TFC. NOTE -- THERE WAS NO TAXIWAY MARKER PRESENT WHEN APCHING TAXIWAY Q THAT COULD BE VIEWED FROM OUR DIRECTION. THE AIRFIELD DIAGRAM OF BOS HAS A 'C' CLRLY MARKED ON WHAT IS CORRECTLY TAXIWAY 'Q;' HOWEVER; ON VERY CLOSE INSPECTION IT REFERS TO 'RAMP C.' TAXIWAY 'C' IS MARKED ON THE AIRFIELD DIAGRAM BUT NOT WHERE IT SPECIFICALLY INTERSECTS THE OUTER/INNER TRANSITION. SUPPLEMENTAL INFO FROM ACN 211028: I FEEL PUBLISHER SHOULD EITHER MOVE THE LABEL 'TERMINAL C' OR ELIMINATE IT; AS IT REALLY ISN'T NEEDED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR RE-ITERATED THAT THE TAXIWAY SIGNS AND MARKINGS AT THE INTXN OF THE OUTER AND QUEBEC ARE POOR AND DO NOTHING TO ELIMINATE CONFUSION. THEY FACE THE TERMINAL AND CANNOT BE SEEN FROM THE OUTER. THE CHART HE USES IS CUSTOM TAILORED BY THE PUBLISHER FOR HIS AIRLINE. HE MIGHT TRY TO GET HIS AIRLINE TO HAVE THE CHARTS CHANGED TO PREVENT CONFUSION IN THE FUTURE.