After more hassle than I expected getting forms to submit with correct values, I now have a flexible and responsive map gallery, with paging features, and the ability to change the sort sequence and the number of items displayed on a page. Next is getting the individual map display code working, which means figuring out how MJ's code works, and trying to fit it into the context of the site.

Note to self: remember, in future, that rather than trying to get a form to submit itself in the old-fashioned manner, it's much simpler to write a bit of script that grabs all the values you want and constructs a GET URL, then sets the location to that. Even simpler might be AJAX, but in this case it seemed overkill so I went the route of a traditional form page. And gave myself loads of trouble as a result (e.g.: if you try to trigger submission from the onchange event of a <select> element, you'll have trouble getting the value of the selected option, and the onsubmit event of the form will never fire).

Tested and working in FF, WebKit (Epiphany), Opera, and IE8.