[Tagging] Mapping metro interchanges

[Ilya Zverev]

Hi,

As you know, I'm interested in formalizing the metro stations mapping. 
Interchanges are an important part of subways, and there are many 
different types of these. For example, sometimes there are two different 
stations with different names that are linked by an underground passage. 
Or there is a single station on which trains come that go on different 
routes.

A few days ago Jerry presented an interesting case that could help me 
(and you) understand mapping interchanges: King's Cross St. Pancras 
station in London. Here it is on the tube map:

http://not.textual.ru/zverik/2/4/kingscross.png

And here's how it looks as a 3D model (4 megabytes image):

http://leewoodprojects.co.uk/wp-content/uploads/2010/04/2955_tfl_kingsx-map_staff-a1c.jpg

As you can see, it has FOUR platforms: for black, blue, light blue and 
ont for three other lines. People spend some minutes getting from one to 
another. But is has a single name and from that it is considered a 
single station by many.

So, should it be one railway=station + station=subway or four?

Ilya