Christian,
You could add these three fields (location, appointment, and nearest hospital) and then reference them from within the form.
Unfortunately, default values can only be literals at the moment, so you'll need to workaround this slightly. For example, you could display the 'default' value and then give users the ability to override this, with a separate hidden value calculation choosing the 'final' value between these two (overridden value if it exists, default otherwise).
If you have a standard plan or higher,
User Case would also be a clean way around to do this. Then you could preload these values as case properties and proper default values, and also update them from within the calculation (IE if the user selects a nearer hospital the default would then be changed to that hospital).
Cheers,
Will