GLF4 FLT CREW RECEIVES A VISUAL APCH CLRNC TO LAS RWY 19R; TO MAINTAIN 4500 UNTIL ABEAM THE 'STRATOSPHERE;' THEN TOLD TO 'TURN BASE NOW;' DSNDS DUE TO ARPT PROX AND IS CHALLENGED BY L30. PLT QUESTIONS 'ABEAM.'

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FLT WAS AN IFR FLT FROM SAN FRANCISCO; CA TO KLAS. RWY 19R WAS IN USE. WE WERE SET UP ON A MODIFIED DOWNWIND TO RWY 19R. WE CALLED THE ARPT IN SIGHT EARLY BECAUSE OF THE EXCELLENT VISIBILITY; AND WE WERE CLRED FOR A VISUAL APCH TO RWY 19R. THE APCH CTLR SAID THAT WE WERE TO MAINTAIN 4500 FT MSL UNTIL ABEAM THE STRATOSPHERE. THE PF AND I DISCUSSED WHAT WAS MEANT BY ABEAM SINCE WE WOULD BE ABEAM OF THE STRATOSPHERE ON 3 SEPARATE OCCASIONS; ON OUR MODIFIED DOWNWIND; ON OUR BASE; AND ON FINAL APCH. AT ALL TIMES WE FELT THAT THE STRATOSPHERE WOULD BE BTWN US AND THE ARPT UNTIL WE WERE ON FINAL. WE WERE PLANNING ON TURNING OUR BASE LEG WELL N OF THE STRATOSPHERE; AND CONSEQUENTLY; PLANNING TO MAINTAIN 4500 FT UNTIL ON FINAL. THIS 4500 FT ALT WOULD PUT US 2300 FT ABOVE THE ARPT ELEVATION. WE BOTH KNEW IT WOULD BE TIGHT PASSING ABEAM OF THE STRATOSPHERE ON FINAL AT 2300 FT ABOVE THE ARPT ELEVATION; BUT WE KNEW IT COULD BE DONE. WELL INSIDE THE STRATOSPHERE; VERY CLOSE TO THE ARPT; THE CTLR TOLD US THAT HE NEEDED US TO TURN BASE NOW. WE DID SO. THIS PUT US ABOUT 2-3 MI FROM THE END OF OUR LNDG RWY ON A R BASE FOR RWY 19R AT 2300 FT ABOVE THE ARPT. WE HAD TO GET DOWN QUICKLY; AND THEREFORE; STARTED OUR DSCNT ON BASE BEFORE WE REACHED ABEAM OF THE STRATOSPHERE. WE FELT THE CTLR WAS TURNING US IN EARLY FOR TFC REASONS; AND THAT THE 4500 FT ALT RESTR NO LONGER APPLIED SINCE THE CTLR WAS TURNING US IN EARLY. HE SAID; 'I THOUGHT I TOLD YOU TO MAINTAIN 4500 FT UNTIL ABEAM THE STRATOSPHERE'; THEN SAID; 'MAINTAIN 3500 FT UNTIL ON FINAL.' WE HELD 3500 FT UNTIL ON FINAL; AND WE WERE HIGH ON FINAL; BUT WERE ABLE TO LAND. WHEN HE TOLD US THAT HE NEEDED FOR US TO TURN BASE NOW; WELL INSIDE THE STRATOSPHERE; WE WERE DEFINITELY ENDING UP HIGH. WE HAD NO IDEA THAT HE MEANT FOR US TO TURN BASE INSIDE THE STRATOSPHERE. WE FELT UNCOMFORTABLE DURING THIS APCH; BECAUSE THE INSTRUCTIONS WEREN'T VERY CLR FOR US AS TO WHEN WE WERE TO START OUR BASE TURN FOR RWY 19R. WE WERE PLANNING ON TURNING BASE IN EXCESS OF 5 MI FROM THE RWY; WHICH WOULD HAVE MADE A GOOD; COMFORTABLE APCH. THE OTHER PLT AND I DISCUSSED THE APCH ONCE ON THE GND; AND WE CAME TO THE CONCLUSION THAT THE CTLR COULD NOT POSSIBLY EXPECT US TO MAKE ANY KIND OF SAFE; STABILIZED APCH MAINTAINING AN ALT OF 4500 MSL UNTIL INSIDE THE STRATOSPHERE ON BASE LEG. WE ARE NOT THAT FAMILIAR WITH LAS VEGAS. WE WERE COMING AT THE ARPT FROM A DIRECTION THAT I HAVE NEVER COME BEFORE. A VISUAL APCH DID NOT SEEM OUT OF THE QUESTION -- WE WANTED A VISUAL APCH. BUT; BEING UNFAMILIAR WITH THE LANDMARKS; TFC FLOW; AND VISUAL TFC PROCS; WE APPARENTLY DIDN'T DO IT RIGHT. SEVERAL THINGS COME TO MIND WHEN REVIEWING WHAT HAPPENED TO US ON THIS VISUAL APCH. THE FIRST THING; WHEN THEY START CALLING OUT LANDMARKS FOR US TO NAV BY; AND WE ARE UNFAMILIAR WITH LCL PROCS; WE NEED TO CLARIFY WHAT WAS MEANT. THE IMPORTANT THING IS TO CLARIFY OUR EXPECTED RTE ON A VISUAL APCH. IF WE HAD DONE THAT AND THE CTLR SAID THAT WE WERE EXPECTED TO TURN INSIDE THE STRATOSPHERE; WE WOULD HAVE REQUESTED A LONG DOWNWIND/FINAL TO MAKE A MORE STABILIZED APCH. IF THIS WAS NOT POSSIBLE; WE COULD HAVE ALWAYS CANCELLED OUR VISUAL APCH AND ASK TO BE VECTORED FOR THE FULL IFR APCH TO THE ARPT. WE THOUGHT WE HAD ALL BASES COVERED; BUT IN THIS INSTANCE; WE DID NOT.