In Endless Legend, cities grow when you use the borough improvement to add a new district to it. It increased the physical size of the city and allows you to gain the benefits of additional tiles around your city.

But it also makes your citizens unhappy. Every new district decreases city approval by 10. And every new city you start (or conquer) also reduces your city approval by 10. When your cities are unhappy, your science and dust generation is penalized. So you need to get everybody happy again and get dust and science bonuses again.

City centers and districts can also be upgraded in power in a mechanic that isn’t really explained well in the game, despite it being extremely important to your city's growth. You may have received a quest telling you to level your city center or a district to level 2 and wondered, "What does that mean?" This system of leveling up your city is an important method of making your citizens happy again. Technologies like the sewer system and spamming bundles of luxury resources are not your only options.

Your city center starts at Level 1. In addition to whatever the tile generates when you founded the city, the city center also adds 1 science, 1 dust, and 1 influence (and takes away 1 food).

Whenever you build a new district, that district does pretty much the same. In addition to the basic tile yield displayed on the map, it adds 1 science, 1 dust, and 1 influence. But it also penalizes the approval level of the city by 10.



But the city center changes if you build four districts on the tiles that directly touch it. The city will then raise up to level 2. This will increase the science, dust and influence it produces. More importantly it now adds +15 to the city's approval. Voila! Your citizens are happier! There's even a graphics change to the city center. You can see that it's taller and more prominent than it was before.

The picture above was a level 1 city center. Here's level 2. Notice the central pillar of the Cultists is taller and more prominent.



But that +15 doesn't counteract the -40 you've gotten from building those four districts. That's okay. The districts level up as well.

A district jumps up to level 2 when it is adjacent to four other districts, or three other districts and the city center. Just as with the city center it will generate more dust, science and influence when it levels up. More importantly, the -10 approval penalty disappears and is instead replaced by a +5 approval bonus. Again, there's also a graphics change to the district making it look bigger and busier than the level 1 districts.

Take note in the changes to the district just to the left of the city center between these two images.





Ultimately what this means is that in order to build a happy city (especially a large one), it should tend to radiate out in a pattern like a circle or triangle rather than snake around to reach certain tiles. The city center doesn't have to be in the middle of the growth, but do keep in mind if you want a city to be large, you need to make sure it's not too bottlenecked by water, cliffs that can't be built on, ruins or minor faction villages, or the boundary to another region. Building by an anomaly may be a boon for a starting city, but beware that its location on the map could actually make it harder for your city to grow after a certain point.

To account for fact that the Cultists can only build one city, they are given the bonus ability to level their city center and districts up to level 3. Everybody else is limited to 2. To reach level 3 in the city center, level up four districts touching your city center to level 2. They get another boost in science, dust, influence and approval at level 3. To reach level 3 in a district, it must touch four other districts that have reached level 2 (the city center counts as a district here). This makes it all the more important for Cultist players to be careful when selecting the starting spot for their only city. You need room to expand in more than one direction.






Also: If you build in such a way that a luxury or strategic resource is within your city limits, you don't have to build an extractor on it. Instead, if you build a borough on top of it, you will automatically begin extracting the resource, as long as you have the right technology to extract it learned. In these cultist images for the guide, you can see buroughs built on titanium and emerald resources. I never bothered with the extractor for either, but I am collecting both after learning the right technology.