Is there any difference in meaning between 哪儿 and 哪里? If not, then how did the two different words come to be employed? Does 儿 have a meaning, or is it just a sound? I know that there are many 'redundancies' in language, but I'm interested in original meanings these words may have had, that led to the redundancy, or anything really, that can explain why there are these two distinct words that are seemingly interchangeable.
Similarly, does the same reasoning govern 这儿 and 这里, 那儿 and 那里 also?