A B737 FLT CREW INADVERTENTLY TAXI THE WRONG WAY DUE TO CONFUSION ABOUT AN ARPT DIAGRAM.

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HVY RAIN SHOWER; LOW VISIBILITY HAD SHUT DOWN RWY 9. ALSO; HVY ACFT/RADIO TFC ON FREQ. ATC HAD GATE HOLD FOR ENG START AND PUSH. RWY 9 REOPENED AND WE WERE CLRED FOR START-UP AND PUSH. AFTER START AND AFTER START CHKLIST; FO CALLED OPS FOR CLOSEOUT (ACARS NO COM). GND WANTED US TO TAXI FOR INBOUND/OUTBOUND RAMP TFC. NOTE: ATC CALLED US A DIFFERENT FLT A FEW TIMES -- IT WAS CORRECTED. THE PUSHOUT HAD POSITIONED US AT THE RAMP AND TXWY C. A HAWKER HAD JUST LANDED WHEN TWR CLRED AN ACR JET INTO POS AND HOLD AND ALSO INSTRUCTED THE HAWKER TO BACK TAXI TO THE RAMP. HE THEN CLRED US TO TAXI TO HOLDING POINT A VIA B. LOOKING AT THE ARPT PAGE I SAW THE TXWY B AND CLRED THE BACK TAXI ACFT AND THE POS AND HOLD ACFT. I THEN STARTED THE BACK TAXI ON RWY 9 TO GET OVER TO TXWY B. I BELIEVE THAT I CLRED THE RWY BEFORE THE HAWKER. AS I WAS CLRING THE RWY; TWR INFORMED ME THAT WE SHOULD HAVE TAKEN 'A' TO THE HOLDING POINT. THE TWR DID NOT SEEM TOO UPSET AT WHAT I DID BUT I TOLD THEM THAT I WAS CLRED TO HOLDING POINT A VIA B. THEY SAID THAT NEXT TIME TAKE 'A' BEHIND THE 'FUEL FARM.' UPON FURTHER REVIEW OF THE PAGE AND THE OTHER PAGES; WE CONCLUDED THAT THE ARPT DIAGRAM IS LACKING DETAIL. THE OTHER PAGE THAT DEPICTS THE PARKING SPOTS SHOWS THE DASHED TAXI LINES BUT IS NOT LABELED. I SHOULD HAVE CONFIRMED THE TAXI INSTRUCTIONS PRIOR TO MOVEMENT BUT I THOUGHT THAT WHAT I DID IS WHAT THEY WANTED US TO DO. THIS WAS THE FIRST TIME INTO SXM IN A FEW YRS. LUCKILY NOBODY WAS IN DANGER DURING THIS INCURSION. SUGGEST A MORE DETAILED DEPICTION OF THE RAMP AND TAXI AREA AROUND THE FUEL FARM.