You've decided you only want to get photos of london. Use the data option of the $.ajax function to pass a location option. Get the location from the data-location on the #tour element using the data method.

theReturnFlight1-6.js

DOM : 
<div id="tour" data-location="london">
  <button>Get Photos</button>
  <ul class="photos">
  </ul>
</div>

JS:
$(document).ready(function() {
  var el = $("#tour")
  el.on("click", "button", function() {
    $.ajax('/photos.html', {
      data: {location: el.data('location')},
      success: function(response) {
        $('.photos').html(response).fadeIn();
      }
    });
  });
});