Hi Nick, I'm not quite sure what you're up to, but if you plot all your cities using the generated lat/longs then right click, and click View Data you'll get a spreadsheet with all the lat/longs Tableau generated. Click upper left corner to highlight sheet, copy and then paste into Excel. Be sure to delete the (generated) in the lat/long field so it doesn't confuse T when you establish a new connection. These new lat/long fields can now be turned into dimensions.
Hope this helps,
I think you can draw a path between cities using generated lat longs. Just set Marks to Line and drag the City field to the Path.
See my example here: