I think you meant size 9 ?
I apologize, the 49 was a very rough back of the envelope number. But let me explain for the benefit of anyone who think communism has a fighting chance in this.
If you run either government and it's legacy card simultaneously, you will find that a Communism governor gives 0.4*2=0.8 production per citizen. Plus 10%, which I forgot to include in my post I'm quoting myself from, you get 0.88.
The first district in a city is pop 1, and every 3 thereafter. Thus, if you place those districts, Democracy will give you 2*2=4 production per district. You have one district per three pop, so that is 4/3=1.33 production (and .66 housing) per citizen.
It follows that as long as you're building more than 0.88/1.33 = ~66% of your districts, democracy will yield more production per citizen than communism's governors. These are late game, tier 3 governments, so it is a reasonable assumption you've been able to get that threshold.
There are only 10 specialty districts available, though.
(Encampment, Campus, Th Sq, CH, Harbor, IZ, EC/Waterpark, Aerodrome, Spaceport, and I'm not sure if the aqueduct counts. I know neighborhoods don't.)
Let's give an edge to the proletariat here and assume the aqueduct doesn't count and that we're landlocked too. And let's assume we cannot into space either. That's 7 specialty districts remaining.
Democracy is giving you 28 production for that. (You need 19 pop to build them all; not an extraordinary figure.)
Under communism, we need ballpark of ceiling(28/0.88) = 32 population to make up that 28 production.
If you pick up the spaceport and harbor, then you need 41 pop as communism to match democracy. Of course, there's fixed yields from buildings in those districts. Let's account for that.
You can actually plot out how much other production you need for Communism's 10% to match the advantage of democracy's districts.
Here's the tabulated data. "Base production" column refers to how much other production a city would need so that the 10% bonus under communism outweighs the democracy advantage. The next column cuts out the 1-3 districts that give production yield: the IZ (assumed to give perfect 12 adjacency, plus 9 for buildings) the encampment (6 from buildings) and the aerodrome (5.) The last column takes that terrain production and puts it in terms of how much production the average citizen working a tile must bring in. I add the district building outputs in IZ first, then encampment, then Aerodrome, while the city has 3 or fewer districts.
4 production average means every citizen is working a grassland hills mine. This is obviously a bit untenable, because this has to be true across EVERY city assuming you have 7 or less, and those mines aren't giving more than 2 food. Remember, you need a governor to get the Communism bonus, and there's only 7. If you have more than 7 cities, then it's starting to look real grim for the hammer and sickle, my fellow workers of the world.
Of course, and democracy is giving you free housing and -25% on gold purchases too. And it has a more versatile card distribution.
)
