Are you using a physics engine? If not then you can't do a platform game
Like mentioned above, you don't have to use a physics engine. I have developed %90 (so far) of a tile based app with no physics engine. It just depends on what your goal is. My game just calculates CGRect's and their positions for collisions. It really just depends on how "physics" apply to your app.
To help with your question, you could just add some tiles (invisible) in the areas where your hero 'can' stand and check if those exist in an update method.
There are some excellent tilemap tuts out there, just search for them.