RWY INCURSION AT MMMX RESULTS IN CONFLICT WITH DEPARTING TFC. ARPT SURFACE MARKING IS AN ISSUE.

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GND CLRED US TO TAXI TO RWY 5 L FOR TKOF HE SAID TO TAXI VIA THE 'B' TXWY. I THOUGHT I WAS ON THE 'C' TXWY AS I HAD MISREAD THE 10-9 ARPT CHART. I TURNED L ONTO WHAT I THOUGHT WAS TXWY B (THE MARKINGS ARE POOR TO NON EXISTENT ON PARTS OF THE ARPT AND I WAS UNFAMILIAR WITH THE FIELD AS I DON'T COME DOWN HERE OFTEN.) IT WAS THE ACTIVE RWY 5-23. GND CTL MENTIONED OUR NUMBER SO I STOPPED IMMEDIATELY. HE TOLD US TO STOP AS WE WERE ABOUT TO ENTER AN ACTIVE RWY. WE STOPPED ABOUT 20 INCH FROM RWY EDGE. AN ACR PASSED FROM R TO L ON TKOF ROLL ABOUT 15 SECS LATER. IT WAS AT ROTATION ALT. AFTER MY KNEES STOPPED KNOCKING I REALIZE SOME THINGS THAT WERE A FACTOR: 1) I HAD ASSUMED I WAS ON ONE POS. I WAS NOT (TXWY C TURNS INTO B LATER ON THE ARPT). 2) TXWY MARKINGS AND RWY MARKING IS POOR. 3) FO HAD HER HEAD DOWN BURIED IN OUR AIRLINES MOUND OF PAPERWORK AND SETTING FMC. SHE COULD NOT VERIFY OUR POS. (ISN'T GOING TO HAPPEN AGAIN!) I DID NOT SEE ANY MARKINGS FOR THE RWY AT B-7. THANK GOD THE CTLR WAS WATCHING US AND I WAS TAXIING SLOWLY! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID THAT THERE ARE VERY FADED AND/OR NO LINES TO DEFINE THE VARIOUS RWY AND TXWY AREAS AT THIS ARPT. THE MARKINGS THAT ARE PROVIDED ARE NOT UP TO THE STANDARD THAT IS USUALLY SEEN AT AN ARPT THAT HANDLES THE VOLUME OF INT'L TFC THAT THIS ONE DOES. THE DISTANCE OVER THE HOLD LINE WAS 4 TO 5 FT. THE COMMERCIAL CHART IN USE WAS NOT CLR AS TO THE DEFINITION OF TXWY C AND B. HIS COMPANY HAS PRODUCED A HANDOUT FOR THEIR PLTS WHICH BRINGS THEIR ATTENTION TO THE TXWY DEFINITION.