As per my understanding, 'at' can be used for streets and specific address etc. and 'in' has to be used for cities.
For eg. at Suite 101, Johnshon Avenue in London.
But I see in a prominent English news paper of India 'The Hindu' that they use 'at' for cities. This is what they publish after the header:
"Printed at Chennai, Bangalore, Hyderabad"
I think it should be: "Printed in Chennai, Bangalore, Hyderabad".
Or it should be something like:
Printed at xyz press in Chennai.