San Francisco-based HotPads, an online mapping site focused on real estate rentals, has been acquired by real estate listings site Zillow. Zillow said it would pay $16M in cash for HotPads. HotPads employees 19, and will remain in San Francisco. Zillow said the acquisition will help it increase the number of leads it sends to landlords, and will help it expand the size of its rental audience. HotPads was led by Matt Corgan.