Why does Metrobits list this city but not that one?
There are definitions, but which system can be safely called a metro or subway, and which not, can be as controversial as urban rail systems around the world are diverse. Some have evolved from trams, others from heavy rail, while still others are monorails or genuine developments. Aside from that, the differences between different modes of transport are fading as hybrid trains make it possible to integrate sections on streets with tunnel and/or heavy-rail sections. When a metro has gradually evolved from former tram or rail lines, it is sometimes even difficult to tell the actual length or date of inauguration of that metro.
The Metrobits database includes full metro systems completely. But it also includes cities with metro-like sections, like tunnels. In that case, only the metro-like section accounts for the listed length and number of stations.
There's also a list of more than 70 metro candidates with more arguable metros as well as proposed ones.
Updated 13 Nov 2011.
This page: http://mic-ro.com/metro/metrocriteria.html
