Best way to handle disappearing search facets?

Question

As part of a faceted search system I'm putting together, I have a series of checkboxes for different neighbourhoods in a city, like so:

[ ] Neighbourhood 1 (50)
[x] Neighbourhood 2 (40)
[ ] Neighbourhood 3 (30)
[ ] Neighbourhood 4 (20)
[ ] Neighbourhood 5 (10)

Now, there can be over 100 in any given city, so showing them all isn't really very practical. The compromise I've come up with (and I'm not very happy with it, as it loses the ability to scan alphabetically) is to have the six most popular neighbourhoods and a link to "See More..."

So far so good. But there are other facets- what should I do when a selected neighbourhood no longer belongs on the ordered list? For example, I change some other facets, now the list above looks like:

[ ] Neighbourhood 4 (16)
[ ] Neighbourhood 1 (13)
[ ] Neighbourhood 3 (11)
[ ] Neighbourhood 5 (10)
[ ] Neighbourhood 6 (8)

...and then, not on this list is my checked neighbourhood:

[x] Neighbourhood 2 (6)

I don't want to remove a checkbox that a user has already chosen, it seems like it will make things very confusing. But what are my options? Has anyone experienced this before? I'm considering either overriding the list order to make sure that checked options are always included in the list, or just making the list X checkboxes longer and including the checked neighbourhoods. Neither seems like a great solution though.

Answer 1

I would include the top 6, plus any checked items. After all if they checked them they are probably more interested in those neighborhoods than they are in the popular ones.

Answer 2

I'd render the checked items at the top of the list. You can skin them differently to indicate that they are not part of the same sorting as the top results.

It is commonplace to show previously selected items in lists this way. A similar problem occurs when rendering selected items in a hierarchical multi-select menu.