MD80 CREW HAD RWY INCURSION AT LAS.

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TAXIING OUT FROM GATE Y TO SPOT X; GIVEN GND CLRNC 'TAXI TO RWY 7L VIA TXWYS D; B; HOLD SHORT OF RWY 19L.' I TAXIED PAST TXWY D ON TXWY S (*THINKING THAT RWY 19L WAS TXWY D) UNTIL THE GND CTLR TOLD US TO 'STOP.' AT THIS POINT; WE WERE ALREADY PAST THE HOLD SHORT LINE ON RWY 19L. AT THE TIME THE FO WAS BUSY COPYING A REVISED DEP CLRNC FROM GND CTL; SO HE WAS NOT ABLE TO HELP WITH THE TAXI. IN HINDSIGHT; IT WOULD HAVE BEEN BETTER TO TELL THE GND CTLR TO STAND BY WITH THE CLRNC UNTIL WE WERE ESTABLISHED ON TXWY D OR UNTIL WE HAD STOPPED AT THE END OF THE RWY. I WAS TAXING MUCH SLOWER THAN USUAL BECAUSE I HAVE TROUBLE FOLLOWING TAXI DIRECTIONS IN LAS. (I HAD EVEN MADE A COMMENT TO THE FO ABOUT THAT THE NIGHT BEFORE; ON TAXI IN.) THINKING THIS OVER; I THINK LAS IS DIFFICULT BECAUSE OF THE LACK OF TXWY EDGE LIGHTS (ON OTHER ARPTS -- EVEN IN THE DAY TIME YOU HAVE THE LIGHT 'POSTS' TO HELP DEFINE THE TXWY. SO WHEN YOU TAXI WBOUND FROM GATE Y; ALL YOU SEE IS A HUGE EXPANSE OF CONCRETE WITH A FEW SCATTERED SIGNS). TO MAKE THINGS WORSE; THE TAXI DIAGRAM SHOWS A COUPLE OF TRIANGULAR SHAPED AREAS THAT WOULD NORMALLY BE GRASSY AREAS ON OTHER ARPTS. I WAS LOOKING TO PASS ONE OF THOSE AS A HELP TO FIND TXWY D. I OBVIOUSLY NEVER SAW IT AND KEPT RIGHT ON GOING.