How do you know what unit you will be placed in during a nurse residency programs?

I am applying to multiple nurse residency programs in and out of state. Some are very unit specific, such as ICU or Labor/Delivery. Others say that they will place new grads in MedSurg, Trauma, Tele, Ortho, ect. I am curious how it is decided where you go in these residencies. Do you apply and hope that you get into the area you want? Or do you just find that out during the interview process? Anyone have experience in nurse residency programs?