US city tours, at intervals, covering large area (5)
I believe the answer is:
tulsa
'us city' is the definition.
(I've seen this before)
'tours at intervals covering large area' is the wordplay.
'at intervals' indicates alternate letters (letters taken at regular intervals).
'covering' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'area' becomes 'a' (maths abbreviation).
The alternate letters of 'tours' are 'tus'.
'tus' placed around 'l' is 'tuls'.
'tuls'+'a'='TULSA'
(Other definitions for tulsa that I've seen before include "part of Oklahoma" , "Oklahoma river port" , "Where in the States" , "An OK place" , "A lust for the Oklahoma oil city?" .)