That's what've done--I've got a collection of Google Maps routes that will handle hotel to zoo and back, and have perused the Zoo and Balboa Park web sites and the transit system's route planner which convince me I needed to rent a car for a day to do the zoo. The city map was just for reserve: if I got myself really lost (not likely), or if the group wants to go wandering further afield later in the week and I want to track where we're going. At that point I'll just be riding along in the car pool.