A "time series" of maps showing rail expansion across the northern Midwest--and the Swedes and Norwegians who followed the rails?

The series of maps I would like to create still lies well beyond my skillset (a reality that is likely to be true for some time), but it was fun to use the "time" function on ArcGIS Pro to get a sense of how railroads were expanding across the country in the mid-19th century.  Given that my mother's paternal side came to the US in the late 19th century from Sweden, I decided to look at the Swedish and Norwegian populations in the 1880 census data, and it was no great surprise to see that Minnesota and the Dakotas had relatively large concentrations of these populations at the time.  This map brings together the Swedish and Norwegian population as normalized across the total population, railroads in 1880, and major rivers.

A couple of things stood out to me looking at this map: first, the Swedes and Norwegians in this northern Midwest area were, indeed, concentrated along both rail lines and rivers--notably the Red River that runs south from Winnipeg (and eventually creates the boundary between the Dakotas and Minnesota) and the Mississippi River, which starts in Minnesota "at a place that you could walk across for five steps down" (Indigo Girls, "Ghost"). In the case of the Red River, I cannot be sure, but it seems that the railroad actually connects the end of that river to the Mississippi River to the southeast.

About a decade after the period represented by this map, my own great grandparents would have traveled from Sweden through Rockport, Illinois, to settle in a rocky area of South Dakota in a no-longer-extant town called Iona, where my grandfather would be born in the early 20th century.  But did the Swedes and the Norwegians follow the rails, or did they create settlements that the railroads then caught up with?  It's not possible to know without finding earlier censuses, but I did use the "time" function on the railroad data to examine where the rails lay in the years before.  Using that function, we can see that it really was in the decade just preceding the 1880 census that the railroads reached Minnesota and the Dakotas.  I've removed the population data since it does not correspond temporally with the railroad dates.

The railroads in 1875:

And in 1870:

With any luck, you'll be able to click through all three maps to get an "animated" sense of the railways expanding.

There are so many limitations to these maps that I hesitate to list them all, but I will point out two major ones that are nagging at me.  First, as Sam mentioned in his blog post, looking at percentages of various populations by nationality does erase total population and can misleading suggest that even sparsely populated areas are well-populated.  I look forward to thinking through how we can account for both sets of information in creating future maps.  Secondly, despite some Googling, I cannot figure out how to export these maps with a legend, so I am ending with that critical nugget for the above maps, courtesy of a screenshot:

Thank you for pretending this it is integrated into the maps.