Cities on the Ring of Fire

I couldn't work out any real pattern as to which cities were included. I think it was largest within each country, so that a place as small as Dili was included but somewhere as big as Nagoya wasn't, but the instructions didn't say that. Also, it wasn't clear how close to the ring of fire a place had to be to be included - why was Auckland close enough but Guadalajara not, for example?