What do you mean by adding an offset and a scale? Right now all coordinate values are around zero, that's how they are generated. The scale is close to one I display in the generator.
Viewing post in 0.7.3: Bug fixes, GeoJSON export comments
If someone wanted to generate multiple cities to place them all on a larger map, they would want to adjust the coordinates to match their larger map. The larger map is going to have it's own coordinate system. Normally i think it would use Latitude and Longitude. The map I have uses pixels x,y of the most zoomed out image.
If was going to do it, I would write a script to import the city JSON and adjust things, someone else may just want to concatinate all the cities in one JSON file and use it like that.