How to show an item's context in a hierarchy

Question

I'm trying to figure out a way to allow contextual navigation to nearby items in a large hierarchy. For example, say my hierarchy is countries, states, counties and citites.

When viewing a county, you should be able to navigate up a level to the state, or down a level to one of the cities in that county.

Breadcrumbs are an established UI that takes care of the up direction of this problem:

USA   —>  California   —>  Los Angeles County

But it wouldn't make sense to put all the cities in LA county into a breadcrumb trail. I was thinking of a vertical layout with the containing item above, and the contained items below, but it makes it difficult to know which one is the "current" item.

Plus, as you can see, it quickly gets out of hand if there are a lot of sub-items (especially if they have long names), and will look empty if there are very few.

Answer 1

An idea - did you consider putting dropdown menus into the breadcrumbs?

It could look like this:

^{download bmml source – Wireframes created with Balsamiq Mockups}