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.
Tedium comes from feelings that you're making a lot of decisions that don't really impact anything. So...
Minimize how many decisions you have to make:
(Of course, try to get rid of the decisions that don't matter, and keep the ones that do.)
- Automate! If you're bored with workers, set them to automate, and make them stop pestering you. There's also an auto-explore.
- Move your units where you really want them to go, not just this turns movement points.
- Fortify or dismiss unit when they're really not helping anymore. They stop asking for orders!
- Set build queue for cities. (thanks @Colen)
- Open the tech tree and tell it to research to something late in the tree. I think with shift or ctrl you can queue up techs as well.
- Puppet Cities - Rather than controlling every city yourself, take over a few, and leave them as puppets. They benefit your civilization, without costing your decision making time.
- City States - For that matter, don't take over city states if you don't have to. They'll help you just fine as they are, with the right convincing.
- Play on faster speeds - This minimizes the extra turns you make decisions for only units, often needlessly.
- Play on a smaller map - Getting places doesn't take a long, and there will be less cities/units overall.
- Play against less opponents - This is best accomplished as a consequence of playing on a smaller map, and the benefits are the same: less decisions to be made.
From my experience, quick games on average are just more fun, because even if the game is bad, its over quickly. Then you start a new game and have a chance to learn from mistakes all the sooner!
Best Answer
City population per city population point does not increase linearly.
Someone went and recorded the city population for cities with points 1-40 for Civilization V: https://forums.civfanatics.com/threads/actual-population-of-cities-in-civ5-i-grew-a-city-from-size-1-to-40-to-test-this.416892/
Basically, a 40-point city has more than 7 times more population than a 20-point one, which has 7 times more than a 10-point one.
Extrapolating, your 60-point city is worth 7 30-point ones in terms of population.