UPDATE The formula has changed as of the March 2011 patch, it is now
(city population * 1.1) + (capital population * .15) - 1
for each city connected to the capital, not including the capital.
- The Machu Pichu wonder increases the modifier by 20%, to
(city population * 1.3) + (capital population * .15) - 1
.
- Arabia increases the constant by 1, to
(city population * 1.1) + (capital population * .15)
(thanks WillfulWizard).
The economic overview also gives a far better explanation of how it is calculated - in other words, this question is now trivially solved by simply looking at that economic overview :)
Original answer below.
Okay, I did a bit more testing, and bwarner's answer is almost accurate:
Each city, excluding the capital, provides (city's population * 1.25) + 0.01
gold per turn. Owning the Machu Pichu wonder increases the modifier by 20%, to (population * 1.5) + 0.01
, for all the cities.
The capital does not provide any gold.
The 1.25 and 0.01 can be seen in the Assets\Gameplay\XML\GlobalDefines.xml
file:
<Row Name="TRADE_ROUTE_BASE_GOLD">
<Value>1</Value>
</Row>
<Row Name="TRADE_ROUTE_CAPITAL_POP_GOLD_MULTIPLIER">
<Value>0</Value>
</Row>
<Row Name="TRADE_ROUTE_CITY_POP_GOLD_MULTIPLIER">
<Value>125</Value>
</Row>
The economic overview also demonstrates these values.
I couldn't find any other factor which affects these values, and I checked different difficulty levels, different distances between cities, different city route type (road vs railroad, road/railroad vs harbor), different city health and whether it is occupied. Looks like it's solely the population.
Declaring war might just be enough. If you can do damage to their military while they're on the offensive (via defensive unit placement on your side and strategic coastal city harassment on theirs), you'll probably end up with a net decrease in their overall science/space production. The CPU will also prioritize building replacement units, even though you are both very far apart. If you set up adequate defenses on your end, even if they come knocking their military won't be able to make much progress.
If you can get a few other nations to join in your fight, they might make the war a little more "real" and bear the brunt of the harassment. You can also use allied city states or Civs as a staging ground, as you suggest. However, you'll have to be careful that your allies don't lose, thereby causing Russia to grow ever more powerful.
I wouldn't bother trying to take territory from them unless you can really cripple their military first - and they'll probably be begging for mercy by that point. As you've noted, trying to land enough units to make progress is going to be painful.
I'm not much for nukes personally, and it's possible that if there are multiple Civs in play that they will ally against you if you commit multiple nuclear atrocities, which could end up giving Russia time to rebuild while you fight a multi-headed war. Desperate times, though...
Best Answer
From the map, it looks like your water route goes north from the city near your capitol, around the northwest peninsula, then hugging the west coastline, swinging around the city-state at the southwest peninsula, and then into your other harbor.
The trouble is that you haven't explored a sea route through uncontrolled areas. Your "invisible trade ships" aren't willing to go into unexplored water to connect your empire together, and aren't able to go through territory that belongs to someone else. Looking at the map, the city-states in the northwest and southwest of your known territory might cut off the straight-water-route between your two harbored cities; the gray civilization (Germans?) to the west of your capitol might also be a problem, if they own all of the water tiles you might go through. You either need to make nice with those two city-states and the gray civilization, or invent Astronomy and expand your knowledge of the Ocean tiles with a Caravel so that your trade can route around the hexes claimed by the blocking city-states and civilization.
Alternatively, you can found a city just east of the labeled city-state in your map, on the water, and put a harbor there. Then your "invisible trade ships" just need to cross a short bay instead of navigating the long way around the continent. (This will depend on whether the city-states to the south and southeast of your capitol own all of the sea hexes on the south end of that bay. You may need to buy a couple of sea hexes quickly to make sure the city-states don't block your access later.)