The digital switchover spectrum plan was based on a 'universal' roll-out of three public service broadcaster (PSB) multiplexes to give analogue equivalent coverage and keeping PSB multiplexes within the analogue aerial group wherever possible.
In addition, spectrum planners incorporated the Ofcom relicensing requirements for the clearance of 14 channels of conventional broadcasting and the conversion of existing analogue channels to digital wherever possible.
This spectrum plan was also based on the transmission of the three commercial multiplexes from 80 sites, and placing these muxes within the analogue aerial group if possible.
The use of spectrum is regulated by international agreement. Within the UK, the framework for spectrum use is set by the regulator, Ofcom.
Spectrum planning is the process by which channels and powers are chosen for each transmitter site in order to deliver the required coverage, within the licence framework set out by Ofcom (and DCMS for the BBC A Multiplex).
Television signals do not respect international boundaries and so the plans must be compatible with, and agreed by, the countries that surround the United Kingdom. This process is called international co-ordination, and the agreements reached are a form of international treaty.
Ofcom has produced coverage figures based on the latest version of the UK's frequency plan. You can find these and further information on the Ofcom website.
For a location to be within DTT coverage there must be enough signal from the wanted transmitter at 10m above ground level in order for the representative installation to work.
There must also be little or no signal from more distant unwanted transmitters on the same frequency to cause interference.