High demand for rentals

[Dave Madoch]

What is the best way to research the demand for rental units in certain neighborhoods? I know the obvious areas like wicker park and bucktown, but those are not in my price range. I am seeking a triplex or fourplex in an area that is on the upward trend. I would like to look on the edge of the city limits but am uncertain if I would be able to keep the units rented. Thanks