Attached Link: http://www.rochr.com/Citylightstransmap.jpg

Like everyone has already pointed out, those lights are done with postwork. First using the method Drawbridgep showed, and then by putting some extra flares here and there with UIC. Ive also made this transmap(just invert it), that can be used for the models. Its a little more awkvard though, since youll have to make the objects hollow, and put some lights inside. Its not as exact as postwork, but it works. :) Also want to mention, that if you use the flares in UIC, use a copy of your original image. Ive just recently noticed, that it can screw up the image quality behind/around the flares. Seems like it only happens with some textures, but still think you should know about it. :)

Rudolf Herczog
Digital Artist
www.rochr.com