I considered that, but this map alone took me almost eight hours and I didn’t have the time to do the rest. That, and I honestly don’t believe that the two series are meant to take place in the same universe, what with the frequent name-dropping of Manhattan and California.
Yep. I kind of felt that I had to do that, because the states in RDR map are so minuscule compared to actual states that they wouldn't even be visible on a map of the country if drawn to scale.
Actually, none of the odd new state borders are rivers. They're all formed by impassable mountain ranges designed to keep the player within the confines of the game map. Your in-game character can swim, so I guess the designers feared that if they used rivers to define the edges of the map, the player would be able to swim across and enter the great unknown.
As for your point about the different geography, much of it arose out of necessity, since I had to place Lemoyne over the site of OTL Louisiana. And Flat Iron Lake really is a lake--according to
this game map which I traced for the wikibox, there is land on the other side of Flat Iron Lake. Since it is connected to the Mexican state of Nuevo Paraiso (portrayed in Red Dead Redemption 1), I figured that the other side of the lake must be in Mexico, and therefore I did not include it in this map.
Not an intentional one, I've never played Red Dead Revolver. But since it's there, sure! It's a reference to Revolver.