I think it's useful to keep in mind how much the projections based on estimates will change as each new year comes out. Last year
jimrtex launched a thread to look at a 2020 map of IA by projecting 2016 estimates to 2020. I used his data and type of methodology to make this map:
At that time the districts had minimal deviations (rounded to the nearest 0.1%): SE +0.1%, NE -0.1%, C 0.0%, W 0.0%.
I updated my spreadsheet to use the 2017 estimates that came out earlier this year. The deviations are now SE +0.2%, NE +0.2%, C+0.3%, W -0.7%. That means the change from last year would be SE +0.1%, NE +0.3%, C +0.3%, W -0.7%. Each 0.1% is about 800 people, so in just one year the changes were enough to cause the 2020 projection for the western CD to dip by over 5000 people compared to the 2020 projection based on the prior year. Think about what deviation in the 2020 projections will be after 3 more years.
IA has very strict rules governing their maps. Based on the number of counties it is statistically likely that no CD will deviate more than 100 persons from the quota even with whole counties. That means it is highly unlikely that any of us will correctly guess today the map that IA will adopt in 2021.
IA is made difficult because it is so thoroughly driven by the cold calculus of geography and population. In states that have humans chop counties to exact equality it is far more likely that we might get close if we can get inside the heads of those who will draw the map.