Population density near the blast sites? Not that they all did the right thing, and real people were absolutely affected. But there is a significant difference.
FWIW, declassified intelligence purporting to show Soviet nuclear targets in Australia suggest that large cities would have been spared direct strikes.
Various other outlets and blogs at the time also made the point that, generally, both the Soviets and Americans avoided population centers as well as (IIRC) decapitation strikes.[1] They focused on strategic military targets, primarily those related to first and retaliatory nuclear strike capabilities. Basically air bases, naval bases (especially submarine bases), and related infrastructure--anything that directly supported the launch of nuclear weapons.
Continental Europe, especially Germany, was an exception because of expectations of immediate ground warfare and the likelihood of tactical nukes. But arguably that's less an exception and more a variation of the same logic.
[1] Decapitation means you've nobody to negotiate with in a timely manner, ensuring the enemy will resort to unleashing every last nuclear weapon at their disposal. Neither side was stupid enough to have unleashed everything at once. All scenarios I've read described an escalation in launches over 1 or 2 days, sometimes longer, with opportunities for negotiated or even unilateral ceasefires.
> suggest that large cities would have been spared direct strikes
That's an Australian assessment of what they expected the Soviets to do in the 1980s.
The actual behaviour largely depends on the specific war-plan and epoch.
Actual Soviet documents from the 1950s show the Soviets planned to 'troll' the West by nuking a few non-Central-Front cities, such as Darwin or Perth, and assessing the response. Would the USA or NATO reply in kind, or back down?
> generally, both the Soviets and Americans avoided population centers as well as (IIRC) decapitation strikes
Not at all. Have a read at these US targets from one of the 1950s SIOPs:
While many are industrial facilities, government buildings and the like, one for each city is simply designated “Population.”
In later years the targetting turned more towards counterforce ( military targets ) as the CEP of missiles crept down into the hundreds of metres. But before the mid-1980s that simply wasn't feasible
If you read "Command and Control" by Eric Schlosser it provides further proof for that. At the height of cold war, US had over 400 missiles ready to strike Moscow directly, purely because of lack of coordination between different forces(so US Army wouldn't share their attack plan with US Navy or the Airforce, so combined they would have launched over 400 missiles at Moscow, a complete overkill).
The British also had about a few dozen warheads and several hundred decoys aimed at Moscow starting in the early 1980s. This was actually pretty sensible: the British wanted an independent deterrent, and with a small force, their solution was to deter the USSR by making sure Moscow would be destroyed. The large number of warheads and decoys was needed to guarantee success against the Soviet missile defense system around Moscow. Smaller players with their own arsenals can complicate things considerably.
A major problem when trying to decode nuclear war strategy is that the rational thing to do after the missiles have started flying is different from the rational thing to threaten beforehand. If your goal is nuclear war, you want to threaten the enemy with complete and utter destruction from which they will never recover. Once it starts, you want to focus on the enemy's ability to attack you further, and probably ignore the enemy's civilian population and infrastructure. But it's hard to present the "total destruction" option as a credible threat unless you actually set up your forces to go through with it.
Of course the UUSR government would have evacuated and dispersed into remote outposts, just as the US and UK planned to. (Although lacking space and possibly security, it's not obvious the UK government centres would have survived for long.)
A more challenging question is - what happens when you get hundreds of warheads detonating in a small area? At a guess that number of explosions would punch its way down into the bedrock. It might even leave a lake of molten crust that would take years, if not decades, to cool.
Detonations in seismic areas might trigger huge earthquakes. (SF would be a very bad place to be.)
Whatever the outcome, it's a fair guess there would be unplanned consequences of all kinds. Most would be very negative, which makes rational (?) planning difficult.
I can only guess that the initial explosion(s) would knock out the systems on ones coming after, so a huge percentage of them would be dead on arrival, unless they were decently spaced out, or somehow all arrived and detonated at the same time. (I guess explosion interference from previous explosion is a serious topic of research when it comes to nuclear warfare, if anyone has any good reading material on this please post)
Key quote: "It appears that two weapons targeted on a silo must arrive at least ten seconds apart to avoid fratricidal fireball effects, and less than one minute or more than one hour apart to avoid fratricidal nuclear dust cloud effects."
