Expressing the location: 哪里 or 哪儿?
When expressing locations, I don't think there is a difference between 哪儿 and 哪里. Both of them mean(to express locations),


where, (in, at)what place
(in, at)every place, everywhere


Your examples show the first meaning. I would like to write a sentence to show the second meaning.


  
  他在哪儿都很出色。
  他在哪里都很出色。  
  
  
  He is outstanding everywhere.


However, 哪里 can mean something else.


Used in a sentence pattern called “反义疑问句"(sorry, I don't know the grammar jargon in English, but I could show you an example about it. Can someone tell me this jargon?) to emphasize your mood of doubt, that you don't believe it. Here, you could also use "哪". Example:


  
  他已经睡着了，哪里会知道我们说了什么？   
  他已经睡着了，哪会知道我们说了什么？
  
  
  Meaning: He has been in sleep already. How could he know what we said. (I don't think he would know)

As an answer to the praises from others, to show your humbleness. For example, I find that you speak Chinese well, so I say:


  Alenanno, 你中文说得挺好的。  


and you answer 


  哪里，哪里。



Literally it means "where, where", actually means "No, I am not so good as you say. I still need improvements". We Chinese usually would answer in this way to show the humbleness.