An operator's network planners need to first decide a new site is needed in a particular area, and a search will be undertaken to identify potential sites.
A new location needs to have a willing landlord, clean access for construction & maintenance, and be suitable for a mains electric supply - all with associated legals.
Once a suitable design for a new structure/tower has been agreed, that needs to pass local authority planning consent and have all legal agreements inplace before site construction can begin.
Out of interest, what visitor attraction are you referring to?
