I'm drawing a map of a real world floor with dimensions roughly 100,000mm x 200,000mm.
My initial code contained a function that converted any millimeter based position to screen positioning using the window size of my pygame map, but after digging through some of the pygame functions, I realized that the pygame transformation functions are quite powerful.
Instead, I'd like to create a surface that is 1:1 scale of real world and then scale it right before i blit it to the screen.  
Is this the right way to be doing this?  I get an error that says Width or Height too large.  Is this a limit of pygame?
If your map is not dynamic, I would suggest draw a map outside the game and load it in game.
If you plan on converting the game environment into a map, It might be difficult for a large environment. 100,000mm x 200,000mm is a very large area when converting into a pixels. I would suggest you to scale it down before loading.
As for scaling in-game, you can use pygame.transform.rotozoom or pygame.transform.smoothscale.
Also like the first answer mentions, scaling can take significant memory and time for very large images. Scaling a very large image to a very small image can make the image incomprehensible.
Pygame Large Surfaces