This was originally a comment, because I had assumed it was considered and not used prior to this question being posted..
At the moment, these are your URLs (with "summary" being a type of action, presumably):
/region
/region/{action}/{id}
Your question is, what should you do if someone tries to access it without an ID, like this:
/region/{action}
I say: Don't allow it in the first place, and shape your URLs conceptually like this:
/region
/region/{action}
/{region}
/{region}/{action}
So with this mapping: {region} -> region/{id}, you get the URLs:
/region
/region/{action}
/region/{id}
/region/{id}/{action}
/region would still go to the same place you intend; a landing page.
/region/{id}/summary does the same thing as your /region/summary/{id}
/region/{id} basically would mean "Get me information about Region {ID}", which could either 302 to /region/{id}/summary, or just return that page.
- Likewise for
/region/summary - the user is asking for information about the landing page. It should return the same thing as /region (or 302 to it, or /region should 302 to here).
RESTful URLs like this are used in web APIs, and they're pretty intuitive, making it a good model for sites that can use them.
Two more sets of examples from the StackExchange API (which, granted, doesn't include /tags/{tags}):
/badges Get all badges on the site, in alphabetical order.
/badges/{ids} Get the badges identified by ids.
/badges/recipients Get badges recently awarded on the site.
/badges/{ids}/recipients Get the recent recipients of the given badges.
/tags Get the tags on the site.
/tags/{tags}/info Get tags on the site by their names.
/tags/synonyms Get all the tag synonyms on the site.
/tags/{tags}/synonyms Get the synonyms for a specific set of tags.
And one from this Edit Answer page (which, unfortunately, doesn't work without /edit...):
http://ux.stackexchange.com/posts/39273/edit
region/{id}? I mean, it sort of means "get me region information about {id}", which in your cause means the summary - unless there's another "base" page for each region, in which case, I'd suggestregion/{id}/summary, so each level of the URL is still valid. – Izkata May 07 '13 at 20:01/regionand/region/{id}. – josh3736 May 07 '13 at 20:04summary. There are other routes that follow the pattern/region/{action}/{id}. – Peter Majeed May 07 '13 at 20:53/region/{id}is the summary, and then have/region/{id}/{action}. Makes more sense semantically. – josh3736 May 07 '13 at 20:56region/{id}/summary, withregion/{id}going to some sort of info page. Think of it this way:{region}/{action}. – Izkata May 07 '13 at 20:58