In Japan I see different markings on platforms. I think these have to do with lining up for each train based on the line type and the number of cars, but I can't seem to ever get it right. How can I read what these mean? Is there a standard (format) that I might see across rail lines?
They seem to have different colors, number-characters, numbers in circles and number pairs.
This is Keikyu main line at KK59, not japan-rail, but I have seen similar markings on JR platforms.
For Keikyu line, it is confusing even for japanese people.
Keikyu trains has wagons with 3 doors and wagons with 2 doors(３ドア, 2-3ドア), thus the confusion.
Please read this page to get an idea if you can read Japanese.
As for Yamanote Line, you will always get it right.
The following is for JR Yamanote Line platform: Wagon 7, Door number 4
Since only Yamanote Line trains are using the railroad, at this spot you always have Wagon 7 and Door number 4.
But take for example JR Saikyo Line.
Since Shonan Shinjuku and Rinkai are also using the same railroad as Saikyo, the markings for Saikyo Line won't match for Shonan Shinjuku Line. This can cause confusion if you don't know which train is for Saikyo or Shonan Shinjuku.
It's complicated, particularly if you don't read Japanese. There are several factors:
The "next train" indicator will tell you what service is arriving and how many carriages the next train will have, shown as eg 6両 or 6 cars in English. For trains with reserved seating, the markings will then say things like Skyliner 6両 4号車, meaning the 4th car of a 6-car Skyliner. Commuter trains usually don't show carriage numbers, only indicators of how far up the platform you should go to get on an N-car train.
The number of doors you usually won't find out until the train pulls up, but this is not an issue for most trains, which only use one type of carriage. The dots in your pictures are supposed to represent this graphically (white: 3-door only, yellow: 2 or 3 doors), but I don't think there's any general standard here.
