Making traderoutes is a powerful feature about freeciv. Making traderoutes have 2 effects. First you get an equal sized gold & science bonus when making the traderoute, then you get the added trade in the cities holding the traderoute for the rest of the game. But there is more to traderoutes, an making them.
When making traderoutes, the bonus is given by the distance between the cities and the combined Trade in each city. But the total trade in a city can be analyzed furhter. Total trade in a city is coming from 1) Base-Trade and 2) existing traderoutes. Base-Trade is the trade a city get from the tiles it use. Base-Trade does not contain the added trade from traderoutes. On the other hand, Base-Trade define the output you get from your traderoutes. High Base-Trade yield high output from traderoutes. The point here is: Maximizing Base-Trade will maximize the output from both existing traderoutes, and the bonus when making traderoute. This is where micromanagement come in as a powerful tool. If you set all workeris inside both cities to work on tiles high on trade before accepting new traderoutes you optimize the trade-bonus. Early in game, this is a feasible strategy. But later the game get more complex, and micromanaging multipple cities before accepting multipple traderoutes is simply not possible. This is where a special "Max-Trade" govenor is extremely handy. By using a "Max-Trade" govenor you can "micromanage" multipple cities in a few seconds..
New players for some reason dont make all (as many as possible!!) traderoutes between their ovn cities before they start doing international traderoutes. International traderoutes do yield more, 100% more for making traderoutes with an other player, and an additional 100% for making them with a city located on an other island. So why is it not wise to rush for international traderoutes, when they apparently yield more?
Lets analyze this situation, and look at the pros and cons with making traderoutes.
Internal traderoutes first!!
First question is: How many caravans do we need? Lets say you have 5 costal cities that you want to celebrate to size 20. Look at the added picture. If you count the lines, then theoretically you need only 10 caravans to fill all traderoutes in all 5 costal. This means that each city need only to make 2 caravans each, and all cities receive 4 traderoutes.
Next question is: How many caravans are needed to make 4 international traderoutes? Then each city need to make 4 caravans each, totalling to 20 caravans! This means that you need to produce 2 additional caravans instead of temples, marketplaces, harbours and other city-improvements that are needed for your celebration. You loose time and momentum.
Secondly, making internal traderoutes is much faster. Moving over your own land, using roads will reduce time to get the bonus and enhanced trade from your caravans. Speed reduce time, and time is the asset. Making traderoutes is allabout speed, the earlier the better, fast is geniuous. Use your roads to get the bonus fast as possible. Shipping caravans around in triremes is logistic nightmare. Triremes move only 3 tiles, the same length as a caravan can move on roads. A trireme can hold only 2 units! Charvels are much better. Charvels can move over deep sea, and cut travel-distance. Charvels can hold 3 caravans. Wait doing international traderoutes until you have navigation.
Third, if you go straight for international traderoutes using triremes, the chances are that the cities you are making traderoutes btween are size 3 -cities. Size 3-cities dont yield much bonus in the first place, due to low Base-Trade. International traderoutes will not make up for the lost time and momentum. Wait to you get at least size 8 cities before making international traderoutes.
What about your allied player?
Lets say your allied player are also having 5 costal cities, and he has only made his first 5 traderoutes, and are in the process of making the last 5 caravans to fill up his cities with traderoutes. Then, if you come with a trireme containing 2 caravans an make 2 traderoutes, how will his layout look like? Basicly, you 2 international traderoutes will block your allie to fill 4 internal traderoutes, just look at the picture. If your allie have already made all his internal traderoutes and are happily celebrating, your 2 international tradeoutes will cancel 2 of his internal traderoutes, making 2 of his cities missing 1 traderoute each. This will mess up his happiness, and mess up his celebration.
And last, if you have an allie, and you both do internal traderoutes, and then share tech, then you get the combined effect of 2 (or more) players making fast internal traderoutes. Tech-race will start, gold be abound and your game will fly. Fast is the keyword.
When to do international traderoutes?
The answer is: When you and your allies have done all possible internal traderoutes, you should make external traderoutes. Why wait this long to make external traderoutes?
Traderoutes between cities that will make more powerful traderoutes than existing internal traderoutes will cancel old traderoutes. External traderoutes with a allie will yield about 100% more than internal traderoutes. Traderoutes to an other island will yield 100% more. The combined effect of alle on an other island will yield 200% more. This is why international traderoutes will cancel old internal traderoutes. Larger cities with higher Base-Trade will also have the same effect. Knowing this, you and your allie can use this to make traderoute twice. Instead of doing traderoutes only 1 time, and get the bonus once, you now can get the bonus twice. And doing international traderoutes between two size 20 cities often give a tradebonus between 500 to 1000 in gold and science from 1 caravan.. So why waste this potential by making international traderoutes for when the trade-bonus yield only 100 gold..
You do the math.