How to create dependent dropdown in drupal 7 content type?
you need to create a tour and location used Node reference module. And automatically change the drop down  option value of location based on tour option value that you can use ajax .  following url help to u 

Dynamic select list in the form (dependent dropdown)

https://api.drupal.org/api/examples/ajax_example!ajax_example.module/function/ajax_example_dependent_dropdown/7