What you're perhaps overlooking is the difference in geography and in population distribution between Australia and the UK.
Australia has something like 27 million people mostly living in the coastal region of a continent.
The UK has almost 3 times as many people, and they all live in a parcel of land about a quarter of the size of NSW.
View attachment 350608
Initially, I was attempting to compare the area England (130,279 km²) with Victoria (227,444 km²) but the entire UK is 243,610 km²,
only slightly larger than Victoria.
Your comparative maps show this quite clearly.
By the way, those red stick pin things, those are some of Australia's terrestrial TV masts.
The UK map of just out main transmitters (not including the small 'fill-in' transmitters looks something like this.
In order to have them this close together, no two locally adjacent transmitters can share any transmission frequency with its neighbours. In addition, there's all the relay stations required to fill the gaps where the geography of the land creates dead spots.
In total, the UK has over 1,000 TV transmitters. Now, the relay stations use a different polarisation. It's vertical. This doesn't make their transmissions invisible to horizontally polarised aerials. It simply reduces the apparent strength that an oppositely polarised aerial 'sees'. Arranging the frequencies and polarisations so that there's no cancellation or other interference is a heck of a planning task.
The same technical problems exist in Australia, of course !
If you check the link in
https://ozdigitaltv.com/transmitters/VIC for the Melbourne transmitters (Mount Dandenong)
you will see that there are four sets of relay transmitters within 5 km of the main towers and each is not more than 5 km from another.
While the highest point near Melbourne
is Mount Dandenong (633 m), that area is quite "hilly" - if not actually "mountainous".
Two "adjacent" sites (Upwey and Selby) use the same set of frequencies but the lower powered Upwey transmitters use Vertical polarization with Selby using Horizontal polarization.
A similar situation exists at Arthurs Seat and Rosebud - about 80 km South on the Mornington Peninsula.
However, the frequencies used there are not the same as those use "across the bay" in Gelong, since this is a clear "line of site" and interference could occur.
(By the way, at its widest East-West point (41 km), Port Phillip is wider than the English Channel, at its narrowest point (34 km)
Anyone for swimming?)
You also wrote
"Australia has alpine regions (and ski resorts) in NSW, but these regions don't support much in the way of agriculture, and so they're not populated in the same way as the hilly areas of the UK."
In this you may be correct.
However, the East cost of Australia has "Tableland" country where "TV Signal Shadows" do exist.
As I was "looking" around on the
https://ozdigitaltv.com/ site
I found this site (
https://ozdigitaltv.com/transmitters/ACT/448-Banks-Theodore )
near Canberra - virtually a Southern Suburb of Canberra
I have no idea of the areas that those small 7 W transmitters are serving on this Dual Transmission site.
Also Jindabyne (https://ozdigitaltv.com/transmitters/NSW/38-East-Jindabyne ) seems to have an additional SMT48 "Channel".
which I would guess stands for "Snowy Mountains TV".
And, there it is - https://snowymountains.tv/
My "point" is that Australian "Authorities" and "Companies" seem to have gone further than those in the UK
to ensure that "most' of the population can receive terrestrial TV signals
and
not be "left out in the cold",
as "ericmark" seems to have been !