The physical paths of Trade Routes

[man_in_finance]

Has anyone seen any info or theories about how the actual paths of trade routes are calculated? There may be some events that alter the path of trade routes between cities, slightly, but I have never noticed anything. Anyway, I appreciate a link if so...

Here is an example where the trade route to Puel Willi Mapu could go through Ngulu Mapu without adding any distance, but it doesn't - it goes just south of it, possible avoiding the rainforest. But if Ngulu Mapu had a trading post it would be missing out on a coin.

Here is an example where the trade route to Mistawasis goes north of the lake and adds 2 hexes to its total distance as well as going over a load of hills, but it has an easier path south of the lake.

Here is an example where the trade route going through Antioch loops around a mine adding an extra hex to the route headed east.

 

[Infixo]

Here is an example where the trade route to Puel Willi Mapu could go through Ngulu Mapu without adding any distance, but it doesn't - it goes just south of it, possible avoiding the rainforest. But if Ngulu Mapu had a trading post it would be missing out on a coin.

If Ngulu Mapu had a trading post it would most likely actually go through it. My observation is that TRs tend to go through cities with trading posts.
That is why I always sent TRs to closest cities first, then further to create a more logical paths. Without that you end up exactly like in your example - with roads 1 tile from the city.
I think if there is no trading post in the city - it is simply treated as an empty tile (which make sense - trading posts are supposed to be "refueling stations" kind of). So, why would I go to an empty tile (=city without a trading post) if this only makes my route longer?

 

[man_in_finance]

If Ngulu Mapu had a trading post it would most likely actually go through it. My observation is that TRs tend to go through cities with trading posts.
That is why I always sent TRs to closest cities first, then further to create a more logical paths. Without that you end up exactly like in your example - with roads 1 tile from the city.
I think if there is no trading post in the city - it is simply treated as an empty tile (which make sense - trading posts are supposed to be "refueling stations" kind of). So, why would I go to an empty tile (=city without a trading post) if this only makes my route longer?

My mistake.. Ngulu Mapu did have a trading post (see the little gazebo icon in the city health bar), so the trader is indeed missing out on an important stop!

 

[Quintus of Mund]

My mistake.. Ngulu Mapu did have a trading post (see the little gazebo icon in the city health bar), so the trader is indeed missing out on an important stop!

But did it have the trading post when the route was created? Sorry not sure if those are active routes or potential routes. Would the path change during the route's running?

 

[kaspergm]

Nice pics, this is one of my favorite rants against Civ6. I hate how the auto-pathing of traders make random, often non-sensical, messy road paths. I could go on about this at lengths, but your post really says it all.

 

[EgonSpengler]

Just looking at that first screenshot, it looks like the trade-route pathing uses movement cost, and avoided the stretch of jungle. If I'm counting correctly, it's 10 movement points to go straight from Puel to Ngulu, whereas 10 movement across the grasslands gets you to the hex just southeast of the city. If you'd pre-built a road through the jungle, maybe even just a hex or two, maybe the trader would've gone that way instead. Of course there's no way to purposefully build a road until the Medieval Era.

 

[Jewman]

If Ngulu Mapu had a trading post it would most likely actually go through it. My observation is that TRs tend to go through cities with trading posts.
That is why I always sent TRs to closest cities first, then further to create a more logical paths. Without that you end up exactly like in your example - with roads 1 tile from the city.
I think if there is no trading post in the city - it is simply treated as an empty tile (which make sense - trading posts are supposed to be "refueling stations" kind of). So, why would I go to an empty tile (=city without a trading post) if this only makes my route longer?

if this is true then we could test this with Rome, they automatically have trade routes in their cities right?

 

[Trav'ling Canuck]

It wouldn't seem so weird if the Trader unit actually moved a set number of movement points per turn instead of moving one hex per turn, but I believe a new trade route always chooses the path to the target city that takes the fewest number of movement points.

Existing roads therefore are often connected to, especially in later eras, since they allow faster travel, even though the unit itself doesn't take advantage of that faster travel.

I don't know that there's any particular effort made to pass through cities with a trading post, but then I don't know that there isn't, either.

 

[Alexadamz]

The first screenshot maybe has some explanation, as that jungle could make trader avoid because of the movement cost. Even then, if we count the tiles and the movement costs, considering that going through a city lets you go anywhere beside it for 1 point, the cost from going from Puel to the tile southeast from Ngulu would be the same through the jungle or through the grasslands beside - one to the Holy Site and wait a turn, then 2 points to cross the river to the forest, 2 movements to the antiquity site there, one to the last grassland beside the hill and wait a turn, 2 points to the hill and 2 more to the silk plantation, making all 6 turns. Through the jungle we would have the same 6 turns, one for each tile in the straight way between Puel and Ngulu, and the last turn to pass Ngulu to the silk plantation southeast.

The others are just insane, in the second screenshot there is already a road connecting Mikisiw to Mistawasis passing throught Hagia Sofia, and in the last screenshot there is also a road there. It just doesn't make any sense at all.

 

[man_in_finance]

It wouldn't seem so weird if the Trader unit actually moved a set number of movement points per turn instead of moving one hex per turn, but I believe a new trade route always chooses the path to the target city that takes the fewest number of movement points.

Existing roads therefore are often connected to, especially in later eras, since they allow faster travel, even though the unit itself doesn't take advantage of that faster travel.

I don't know that there's any particular effort made to pass through cities with a trading post, but then I don't know that there isn't, either.

I built a road with another trader (you can see on the map) and now that same route option has changed to follow the road. (Although there is no guarantee this was the cause of the change - it might just be the algorithm has some stochastic route planning element and worked differently here)

I know from having worked with AI that route planning is difficult task computationally. Of course there are algorithms that find "optimal" routes but what are the parameters that define "optimal" in these scenarios? Gold (via passing through trading posts in foreign cities), movement costs improvement for units, etc.? In fairness I think civ vi does a fairly good job with it given its complexity and having to limit computational power for other areas!

There are the scenarios when multiple paths might exist that are equally valid choices and the AI just selects one (who is to say I would not rather go via Frankfurt to Dortmund, if Reyna was in Mbanza Mbata):

So, if anyone wants an idea for a mod that I would definitely use: Trader routing with custom inter-route destinations. I might even loop my traders around lots of foreign trading posts!

 

[kaspergm]

So, if anyone wants an idea for a mod that I would definitely use: Trader routing with custom inter-route destinations. I might even loop my traders around lots of foreign trading posts!

I've said this many time before, but I guess it doesn't hurt to voice this at any given opportunity, so: We need some sort of "connect-the-dots" feature to lay out trade routes. It could be an advanced option alternative to the auto-pathing for those who don't care for it. So in your case above, we need to be able to pick different paths, for instance:
Start - Mbanza Mbata - Dortmund (as shown)
Start - Mbanza Mbata - Frankfurt - Dortmund
Start - Mbanza Mbata - Frankfurt - Mohenjo Daro - Dortmund (if distance allows it)
Etc.