How to measure city separation?

[Sparkuss]

Sorry but need to ask a psuedo-noob question.

In all the strat threads on squares between cities, where are you counting from? City center to city center? or Size One city boundary to next boundary?

I made transparent plastic templates with the max city size when I used to play CIVII and CTP. If someone can tell me the answer I can tweak them again for CIVIII.

Thanks

[notyoueither]

City center to city centre is the usual basis of measurement.