I am new to English language. I have seen many times when the word "in" is used to explain an area "at" is also used following it.

For example:

>I am living in Tokyo at Koganey.  
> He is staying in Sydney at Camden.

I want to know that why it can not be written as: 

> I am living in Tokyo in Koganey.

Is there a rule to follow when writing like this?

I would be grateful if you could give a clear explanation about this.