Bonuses based on number of connnected (and eventually foreign) cities are a good idea! Though I'd prefer them being

rather than straight gold, since we're replacing trade routes that gave

.
I have to agree with noyyau on this
And I would like to make a last stand for TRs, because even if we proceed on this path to exterminate them, I don't think it's the best solution, and I would like to make a significant change on its procedure of calculation to make the game faster, instead of just getting rid of them. But as I'm no modder (yet, hopefully

), I have no idea how to do this, so I don't want to stop the ideas from the real modders and fathers of this mod.
But I'm an addicted player, who tried to understand the game as fullest as possible to play the most realistic of games. So here it begins:
A guide to TRs.
Macromanagement
First of all let's take a look at a marvelous advisor:
The Financial Advisor. But actually its INFO tab. On INFO you may check several informations, including how much

all your TRs added together yield with each nation separately (including yourself).
E.G.: You are Rome, in a massive continent and then you check your yield in routes:
Rome: 1100

Arabia: 200

Khmer: 500

Ottoman: 120

Some others: 10 - 50

Many others: 0

Total: 2500
This way you know 2 truly important informations: Who is(are) your best trade partner(s) and What's the difference between internal route

and foreign route

.
The first info is good to put an extra weight to make a decision of DoW. In this example declaring war on Khmer will take a serious economic repercussion on our Empire, while the Ottomans probably won't.
Have in mind declaring war don't just remove that
you have with someone, but rather change all TRs to new ones that may give the same or lower profit then before (never higher). Normally the best partners are the hardest to replace, and the losses will be bigger. Mediocre partners usually can be substituted easily. Usually the number of possible Trade Partners that are unused being bigger, and the number of internal routes
yield being bigger mean your losses on DoW will have less impact. The less unused possible Trade Partners and the less internal
yield, the stronger impact a DoW will have.
The second info is great not only for what has already been explained above, but also to see your reliance on foreign nations. The bigger the ratio between Internal and Foreign

the bigger your economic independence from the foreign (a good situation to change to a No Foreign Trade Routes civic). The less this ratio the more you economically depend on other nations.
This

represents taxes from private established trade routes, something the state can't directly control. And the game was truly nice in this mechanic by making it give
always the best Trade Routes there are as if our private entrepreneurs were incredibly smart and always striked the best deals (but in terms of memory usage they have been terrible).
Micromanagement
TRs always have a base of 1+

and it's a fractional number (maybe there is the option to have it as an integer? I don't know, I always play with it as a fraction). Over it several modifiers are applied and may make this number quite big. The idea is that for every TR you get a

bonus as it was an extra tile. It's value ranges more or less like a normal tile, but TRs only give

and it's never 0. In micromanagement,

is the least of our problems because it doesn't affect the city itself, but the whole empire, differently from

and

. In late game these values can reach unthinkable caps, but I never played AND after the Renaissance, so I would guess, as in LoR I've already seen 15

routes, AND possibly can reach up to 30

routes. Of course on average it would be a lot less, but that is a good peak I think. If on LoR the average could reach 8-9

AND may get to 15

average I would guess. And as AND may have double the max TRs then LoR, in total yield we can actually double it too. So it keeps with tile advancement in

, but reach higher peaks if managed well.
Basics
TRs are established if:
- You have the other city on your possible trade map chart (this includes all possible tradable tile connected by adjacency to another possible tradable tile). This means starting from your capital, every tile connected by a road is on your trade map chart, rivers (with a certain technology) serve as roads, coast tiles (with a certain technology) also count as roads and ocean tiles (with a certain technology) are the last to be added (maybe AND futurism has something that enables trade in all tiles? I didn't explore the game as much) to your trade map chart.
Black tiles are not tradable tiles, and so if you didn't explore the map you can't trade with those cities on the black. Enemies (barbs too) cut tiles from possible trade tiles and consequently may cut your connection with other players.
- You may actually make TRs (in AND you start with 0, Wheelwright Building and Trade Tech open the first possible TRs). For Foreign ones you must stop using the starting civic that cuts foreign TRs.
- One of the diplomatic options of open borders starts the possibility of actually make TRs with someone that is on your trade map chart (not sure which one in AND). So logically there is no TRs between enemies at war.
- And finally it's one of the X best TRs available for you, X being the total number of TRs you can make globally. So if you have 30 TRs available, and wonder why you have TRs only with the AI superpower it's because they are the best available from all that you can have (including national and foreign).
Modifiers
And what do you have to know to see who can be a good TR partner without having to try and reload with everyone? So here are the Important Modifiers:
- If the guy is majorly overseas to the majority of your cities;
- If his cities are big (10+ pop) or he is far away*;
- If you are at peace for a long time (max 50 turns, above 50 everyone has the same bonus on this field);
- There are other bonuses related to Advanced Economy that I didn't discover yet, but the above 3 are probably the most important anyway
*This is an exclusive or, foreign city pop and distance don't stack, they are separated values, and the highest is chosen. I'm not sure the relation between both, so to see how each yield (I just know the pop to be considered must be above 10) is still a mystery to me. But if you happen to see a truly distant partner with lots of big cities, you know from one way or the other he is a good trade partner

(and you may always check and reload).