"The key is on the chair."
Translation:Aia ke kī ma ka noho.
Xana's question and Kekoa's reply are from almost a year ago, but there is another reason to use "ma" instead of "i" after the word "aia."
Instead of "aia i hea?" (where?), you can ask "aia iā wai?" which is asking who has possession of something. "Aia iā wai ke kī?" (Who has the key?) So replies would always use "i" or "iā" such as: "Aia iaʻu." (I have it.) or "Aia i kēlā keiki ma ʻō" (That kid over there has it.)
That means that if you say "Aia ke kī i ka noho," it ends up sounding like "The chair has it" instead of "It's on the chair." Even if that is a grammatically correct sentence, it just sounds weird. So after "aia," stick with "ma" to indicate location unless you actually do want to say who has whatever you're talking about in his/her (its?) possession.
Now I wonder if anyone will read this after almost a year. Pehea lā. Also, I gave a better explanation under the statement "Aia ke kī ma ka papahele" (The key is on the floor.) if anyone is interested.