Variable that change building outside of cultural borders?

[The Butler]

Why can roads be build outside of cultural borders but other tile improvements cannot? Is it possible to change this so that forts can be built outside of cultural borders?

Additionally what files govern city creation? the <ifound> tag is what creates a city but is it possible to configure a unit to create say a fort with a cultural radius of 1 or is this something that is python rather than xml based? If so does anyone know roughly what file to look at

Thanks