Learn something new every day...
Huhuhu, I'm getting a lot of likes today.
It is also possible to break down Sitting Bull's total empire production by analyzing the Production Graph on a per-pixel basis.
From demographics on T63 and T64, we know our empire produced 28

(Million metric tons)
Microsoft Paint says the graph is 21 pixels per

tall, so we can label Sitting Bull's production every turn.
Sitting Bull Total Empire Production
from all Cities [

into Workers + Settlers and whips don't count]
T55 - 5

(After hitting the enter button on Turn 55, Sitting Bull's empire got 5

from tiles)
T56 - 5

T57 - 5

T58 - 6

T59 - 5

T60 - 5

T61 - 5

T62 - 8

T63 - 8

T64 - 9
This compares to the hammers invested in a unit/building in Cahokia and Poverty Point from the

screen.
Cahokia (Capital) 
T55 - 51 (On Turn 55, Sitting bull had 51

invested in a Settler)
T56 - 57
T57 - 63
T58 - 69
T59 - Building something new
T60 - 15
T61 - 18
T62 - Building something new
T63 - 4
T64 - 3

T65 - 9
Poverty Point 
T55 - 3
T56 - 4
T57 - 5
T58 - 6
T59 - 8
T60 - 10
T61 - 12
T62 - 14
T63 - 16
T64 - 18
T65 - 20
I don't see any hidden Iron tiles in Sitting Bull's land that we can see.
It is all very interesting.
The demographics table reflects numbers instantly.
So do the population numbers. They are also instant.
The graphs reflect what numbers actually got processed last turn.
Cahokia Population
T55 - 2
T56 - 2
T57 - 2
T58 - 2
T59 - 1
T60 - 1
T61 - 1
T62 - 1
T63 - 1
T64 - 2
T65 - 2
Poverty Point Population
T55 - 1
T56 - 1
T57 - 1
T58 - 2
T59 - 2
T60 - 2
T61 - 3
T62 - 3
T63 - 3
T64 - 3
T65 - 3
Conclusion
Poverty Point is producing 2
per turn and working water tiles mostly at Size 3.