How do I choose an urban planning focus?

I'm currently an undergrad student majoring in Finance/Economics. I am interested in going to grad school for Urban Planning but have realized that there are many different focuses (Econ, Transportation, Historic Preservation, Architecture, Urban Studies) and I have no idea how to choose one. It looks like you kind of have to decide what area you want to choose before you can choose a school since each school offers different focuses. Anyone have any advice on how I could learn more about them and eventually decide which I'd like to focus on?