Perhaps, several terms being mishmashed together ?

Gates center track is the 2nd version of their belt

Drive center line ?

that is determined by where the Hub places the toothed ring,

you adjust the crank part of the chainline to match It. ..

chain line is same thing were it another IGH , with a chain.

Compatible frames .. have to Open the rear triangle , to let the belt pass through, some how.

many other frame builders can offer a useful frame, but may not be as cheap
as the one REI brings in.

http://www.rei.com/product/825377/no...tham-bike-2013

interesting combination .. with continuously variable Gear Hub