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
http://drupal.stackexchange.com/questions/10112/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