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When the aircraft is readying to taxi, the ATC asks them to proceed to some runway number, say runway 09. In big airports, how do the pilots identify the correct path to their runway?
Does the ATC guide them? Or do they get a map of an airport chart?
Source: wikimedia.org
Guiding is called progressive taxi and can be requested. A follow-me car can also be used to guide the plane. In some airports the follow-me car is mandatory, along with its fees.
In most cases the pilots use charts. Either paper or electronic. Some electronic charts offer a moving map feature, whereby the crew can see their position on the map.
Lastly, there's the new follow-the-greens (video link), in which the ATC programs the taxi route and the crew are then guided by smart green lights. Follow-the-greens cockpit video / ATC audio in Singapore Changi can be seen here.
In all cases, except for follow-the-greens, the route is given. It's worth mentioning that the taxiways are marked by signs as well.
Coming soon by 2020 (2021 update: it's now ready for deployment; full benefits by 2023) is the taxi route display for pilots, in which the cockpit displays draw the taxi route via ATC datalink. See possible interface here (Boeing). Airbus interface below:
Source: SESAR JU D-Taxi provides datalink exchange solutions for flight crew and controller during taxi, YouTube
Almost always pilots use a chart, ie a map which shows the airport from the air. Runways are numbered according to their magnetic bearing (runway 22 is roughly aligned to 220 degrees magnetic for example) while taxiways are lettered. As an example see the chart for La Guardia.
A pilot would be given a taxi clearance which gives an end destination and a set of taxiways to take in the order they should be taken. For example, a pilot parked near the fire station might be given a taxi clearance like "US123 taxi to runway 31 via Foxtrot, Alpha, Lima, Bravo and Zulu." The pilot would look at the map and see the paths to take.
While taxiing there are signs on the ground which assist the pilot in navigating the taxiways. Some give directions, some indicate places where ATC have to clear a crossing.
Occasionally a pilot will need additional guidance in which case they can ask for a progressive taxi, where ATC will guide them through the airport, but this is rare as it is very labor intensive for ATC. There are also vehicles with "Follow Me" signs and lights which can be sent as well (these vehicles need clearances too).
It is good practice for pilots to study the ground plan for any airport they plan to visit so they know what to expect when they get there, and have the plans available in the cockpit.
'follow-me' cars, and progressive taxi can be used, but at a towered airport, ground control will give you that with your taxi clearance.
"United 2133, Laguardia Ground, taxi from the commercial ramp to runway four using taxiway alpha, echo, and bravo."
Using a taxiway diagram from the A/FD, you would locate your position on the plate, the taxiways in question and from there determine the route you will take. In this case you'll turn left from the ramp heading northwest on taxiway A, then take a right on taxiway E, then take a left on taxiway B.
If you are unfamiliar with the airport, you can then request a progressive taxi."
"LaGuardia Ground, Beech 2375 X-Ray, Unfamiliar with the airport layout. Request progressive taxi."
NOTE: This will annoy controllers at busy airports if you habitually do this as it is expected that you have this information ready at hand before you call ground requesting a taxi clearance.
The 'follow me' vehicles are usually used for quickly routing VIP or special use aircraft to a section of the ramp e.g. Trump's 757 to a section of the ramp cordoned off for a campaign rally, etc.
Very often, the instruction is in the form "Taxi to holding point RWY 24 via H, L, cross RWY 13, K, B." The letters are the names of the taxiways.
The pilot then looks into the airport chart and follows exactly as instructed. You must hold short before crossing runways, unless they are used as taxiways.
It is easier when the instruction is followed by "Follow the follow-me car.", then you just follow the car.
They have the charts in the cockpit, either in electronic or in printed format.
As an example, see page 83 of this pdf, showing the charts for Amsterdam's airport (AMS/EHAM).
ATC will not only tell them to which runway to go, but also which taxiway(s) to use to go there.
In pilot training, it is taught to have a diagram of the airport and to study it before flight.
The tower is usually willing and able to help (as described in other answers: progressive taxi) but depending what airport you're at, you may have to act like the pilot in command and know what ATC is talking about. You'd need to know where to taxi and you'd need to do it fast.
Having the diagram of the airport is necessary but you also need to know it. Sometimes taxi instructions change midway through taxiing. You get the point.
The bottom line: pilot in command has to know where and when to taxi. The rest of it is nice-to-haves.
