Trade route routing algorithm

I am curios to know how the route to a city is being calculated because i noticed that in one of my games the route took the longer way around.

I started the trade route from the lower right city: Chapultepec and sent it to Delhi. The route chose to take the road through Geneva even though it is 1 hex longer that way (9 hexes) compared to the direct route of 8 hexes. Now, i do believe that Delhi already had a road to Geneva from a current or previous trade route they sent there.



Is is calculated by pure distance or is the travel time also factored in?

 

It's because once the trade route to Geneva had been made, it created a trading post which extends trade routes and also reduces the time through them.

 

I wish you could manually alter the trade routes... Not every road should go directly from city to city.

 

I may be mistaken - and i'm sorry i hadn't mentioned it, i didn't think about the possibility of what you said - but i remember i had units with which i wanted to attack Delhi and i had no road to Dlhi, so because of that i wanted to make a trade route to Delhi first, until the units were being moved from the other side of the continent (which would have taken at least 10 turns). So i started the trade route to Delhi with the detour that i mentioned because i decided to also ally the CS and move through there territory instead. Of course until the units arrived i also made a separate trade route to Geneva. I am not 100% sure of course so i will watch out for what you mentioned in the next games.

 

2 things that really annoy me about this

1. A trade route of mine will go through a city state and if I loose ownership I am without a unit road for quite a while
2. A trade route will go by sea if faster but I really want a road.

I would love a couple of new route options

1. Do you want to the route to go by land or sea?
2. Do you want the route to go directly to the city or link up to another route?

 

I don't think they should give options.... instead they need to give more benefits
(ie sea routes should be preferred, but should give bonus gold for their reduced travel costs..something like 0.1 gold per sea/water tile)
(trade routes should favor going over existing roads, and through cities that have trade posts)