Well, maybe not IN the shell, but near it - better have it visible through its entrance. :9
My current exterior visregion (which may become unnecessary, should global ones be added), extends a little outside the shell, into the street, at least and I hope this encroachment doesn't offend anybody. :)
(It is also perfectly trianglular in shape, to make it as simple as possible - I'd wager a guess that all the various regions for every shell and every street, is going to add their own collison/containment detection overhead.)
I don't know about others, but I mean to have a severly detail-reduced version of the exterior parts of my shell, for viewing from the tower, or neighbouring shells with tall structures (placed in the shell's statics page...
(Hmm, just remembered another thing, should we get visregions as part of the standard city layout: I couldn't do cross-page references to my visregions, when I first started fiddling with them, so I wound up duplicating the SV:s: one copy on shell's normal page and one on the statics page. Has others succeeded where I failed? Hmm, maybe it was because I used the shell-page-number-plus-1000 convention and maybe then it would have worked, had I only not had the pages spill onto different sequence prefixes?)