For those not familiar with where cities are located in the US, that map is basically a population density map of the US. High population density regions are blue, low population density regions are red. This is true even in "deep red" states and "deep blue" states.
The founders knew this divide would exist, because the same basic divide was there 200+ years ago (different parties and party names, but the same rural/urban political divide). They purposely chose to design the electoral college system in a way that gave rural regions a significant say in political outcomes even when their population densities are much lower than those of cities. They also purposely placed seats of government away from major cities, for much the same reasons.
The country may be more polarized today, but the color pattern on the map is not new.
The electoral college was originally intended to have the states appoint some grandees who would get together and discuss whom the best candidate for president would be (for an election system that actually works like this today, imagine the papal conclaves). This system worked like this approximately once, and failed catastrophically by the fourth election, which prompted the slight adjustment that we see today. Electors weren't regularly selected by popular vote until after that change, largely complete by the 1820s.
Meanwhile, the reason for the electoral allocation reflects one of the most fundamental compromises in the design of the federal system: is the national government be representative of the people, or is it representative of the states? The answer is it's both--that's why there's one house for the people and one house for the states (the Senate). And the number of electors for the president is similarly a compromise, giving one vote for each member of both houses. (Again, recall that senators were not elected by popular vote until the 20th century).
There was no concept of a rural/urban political divide, because urbanization really wasn't a thing in 1787. The overarching concern of the people who wrote the Constitution was balancing the powers of a state like Virginia versus Rhode Island--the small state/large state divide is the major focal point of discussion--although there was also a contentious issue over the role of slavery (of course, in 1787, most states were slave states--only Massachusetts had fully abolished slavery by that point, although the rest of New England had just adopted a gradual abolition program) which yields the ⅗ compromise.
> They purposely chose to design the electoral college system in a way that gave rural regions a significant say in political outcomes even when their population densities are much lower than those of cities.
This is a myth. The electoral college as originally conceived simply granted a elector count[1] to the states and let them decide how to allocate them. It had nothing to do with urban/rural divide, which barely existed at all outside of the three (!) states that actually had cities of meaningful size.
The interpretation you're proposing is decidedly modern. It's a retcon intended to justify the fact that "red" states in the modern electorate are clearly wielding outsized influence. But even that has only been true for 2-3 decades.
[1] What asymmetry existed was actually because of the way senate seats are allocated. Its effect on presidential elections was essentially an accident.
I am skeptical of this claim because in the 1700s the urban population would have been minimal compared to what it is today. A large majority of people were employed on farms.
Wall St was an actual (medieval) wall until the turn of the 18th century. It's at the very south of Manhattan, a ten minute walk from the tip of the city it was built to protect.
NYC's postal names are a mess: Manhattanites can write "Manhattan" or "New York". Brooklynites are supposed to write "Brooklyn." Queens denizens write the historic names of the farm towns that used to be there. "Astoria" is actually part of New York City, even though seeing a letter addressed there might make you think it's a town upstate.
The postal service is older than the current boundaries of New York, and they never updated the mail routing to reflect the unified city.
Before the bridges were built, much of what's now NYC was very rural.
I believe the medieval era ended in the 15th century, but the wall was built in the 17th. So actually the wall would have actually been a colonial era wall, if going by eras - not to mention the construction style was actually more reminiscent of colonial era structures rather than medieval.
Seats of government necessarily become cities. You don’t create a new city to keep power away from cities. State governments tended to be put in central locations for the convenience of all urban and rural dwellers, and away from existing power centers to avoid concentrating power with the wealthy.
The electoral college demands proportional representation in presidential elections. It says nothing about whether the electors are rural or urban dwellers. In fact, proportional representation weakens the power of less populous states.
The original unicameral continental congress with only a senate gave more power to less populous states, but the founding fathers found it effectively gave any single state veto power, which was counterproductive, and hence the great compromise was passed creating the House.
The map of where slavery is allowed corresponds pretty well with the areas that are rural, as you don't need slaves to work the fields where there aren't fields, and slaves are a poor labor source for the more differentiated and fluid industries in cities (there isn't enough liquidity for them to adapt to changing economic conditions, as the slaves are property of a single owner and their labor isn't traded on a free market).
This is not true at all. Slavery wasn't allowed in the rural north. And in the south, slavery was part of all sectors of the economy. Slave factories were even a thing. Furthermore, slave labor could be traded on the market just as well as any other labor. There was nothing stopping a slave owner from renting out his slaves a contract labor. If the civil war hadn't happened when it did, southern slavery would have been an industrial horror.
