Rule Clarifications

[maddox]

I will also toss out the fact that water transport is extremely more efficient than land transport.

Not a lot of historical big cities that ain't supplied by water untill the 18th century.
And a boatload of canals dug over the millennia. 

On land, rail is ~6-8x more efficient than trucks. But that's a developed province.Undeveloped provinces will have some trade routes which may be drivable/developable, so some truck traffic (depending on tech), but mostly pack animal
The ability to widen/improve would be terrain limited.

We're 191X in the Nverse. Peking to Beijing was done in 1907. But only thanks to camels...

All just considerations with long supply lines.

Great Empires put a lot of effort in good internal transport. Look at the Brits.  Untill they lost to much oversea trasport capacity, they had a world spanning empire.
The Mongols were all about fast and light transport.  The Romans and Inca put their eggs in the Roman/Royal roads.
The Fertile cressent had the advantage of the big rivers. Nile, Tigris and Euphrate.

[Kaiser Kirk]

We do presume the NPC nations are developed and more robust than historical, so world wide there should be more internal infrastructure.
Likewise many of the undeveloped lands are presumed to have little kingdoms and be a bit more organized.
One can generally presume there's at least a pack trail across the province, and possibly a wagon road.

However, we've also assumed most of the NPCs were not very active internationally, and many of the historical trade routes to the Americas involve nations that don't exist in N7.
Which is part of why only small coaling stations are at most of the "Port Symbols" in undeveloped areas.


As for roads....The Mongols, Romans and Incas are late comers.
The Persians built the Royal Road in the 5th Century BCE, 2400 years ago. https://en.wikipedia.org/wiki/Royal_Road
While the Silk road (more of a trade route) started in the 2nd Century BCE...shortly after the Parthians came to power in Persia. https://en.wikipedia.org/wiki/Silk_Road
But there is grave good evidence the steppe dwelling Iranian peoples much earlier than that may have traded with China. Those were also likely the same peoples that gave rise to the Amazon legend, as many of the graves have women with armor and weapons.