Presidential party preference post WWII

Land doesn’t vote.

The National Popular Vote bill would guarantee the Presidency to the candidate who receives the most popular votes in all 50 states and the District of Columbia. It has been enacted into law by 17 states and DC with 209 electoral votes. It needs an additional 61 electoral votes to go into effect.

https://www.nationalpopularvote.com

Yeah but the people who own land matter more. The 17 that passed this are probably not the 100% red states here so this is gonna go nowhere
- It won’t matter if those who enacted total more than 50% of the electoral votes.
  As of April 15, 2024, the National Popular Vote bill has been enacted into law in 18 jurisdictions possessing 209 electoral votes, including
  6 small jurisdictions (District of Columbia, Delaware, Hawaii, Maine, Rhode Island, Vermont), 9 medium-sized states (Colorado, Connecticut, Maryland, Massachusetts, Minnesota, New Jersey, New Mexico, Oregon, Washington), and 3 big states (California, Illinois, New York)

The parties switched up during the Civil Rights Movement. Why does the map include both before and after that time?

The Civil Rights movement is what caused Republicans to move towards business and away from helpful social policies. The Democrats saw the shift as lots of their own rank fled to join the Goldwater Rs and pivoted to grab the underrepresented folks. This broadly created the current business focused Republican Party and the social focused Democrats.
- The business part is not true. Hoover was a Republican President who loved big businesses. FDR was a Democratic President who enacted many policies to help poor people.
- The republican party has been pro big business since the late 1800s. As the other person has mentioned, you can see the parties' modern economic stances by the 1930s. The Civil Rights movement just shifted them to the Business and Racism party.
I think you are thinking of the whigg party and the democrats. That was long before the Civil Rights Movement. The big shift during the time was black voters switching to democrats because of republican speeches against the Civil Rights Act. https://www.studentsofhistory.com/ideologies-flip-Democratic-Republican-parties
Switched as in the spiderman meme. America doesn't have a left and right party, you have two rightwing ones.

I feel like when comparing over a such a vast time scale party affiliation becomes less useful as a metric.

Society and mores have changed so much over the last 80+ years that it's better to ask about specific questions or habits like: Do you support a smoking ban in public spaces? or Schools should provide free meals to students: yes/no and see how the answers develop over time.

Similarly erratically, Nate Silver of 538 fame was pretty sure American Democrats would be more hesitant to wearing masks during a pandemic than Republicans would be because Democrats were known for more of a my-body-my-choice philosophy.
- I read his personal blog a bit recently, and I was surprised by how much he talks about the "woke left". If I ever met him, I'd want his take on all the statistics that, to me, make that group out to be mostly a straw man.

Keep in mind not all states were states at the conclusion of the war. Only Alaska and Hawai'i, but still, they lost a few years.