By default, the Maps app in iOS always gives you driving directions. For people that live in larger cities, sometimes walking directions are more convenient and what you actually use most often. Instead of having to choose walking directions each and every time, just tell Maps to load them by default. Here's how:
That's all there is to it. Maps will now default to providing walking directions instead of driving until you decide to change it. I'm not sure why Maps doesn't let you default to public transit directions but hopefully this is something they'll add in a future update. It's certainly odd that it's just left out for no apparent reason.