Buildings only effect the population over a certain distance. Place a theatre too far away from your citizens and they will see no entertainment benefit. The same is true for all types of buildings: if the clinic is too far away then the doctor won't be able to properly make his rounds and so people will become ill. You also can't put certain buildings too near your accommodation, for instance a reservoir is deemed an ugly building (even though it actually looks pretty nice) and as such it lowers the 'desirability' of an area. To counter that you need to build pretty things like Plazas and bushes to keep your people happy.
The constant struggle of maintaining a balance within your city will either make or break this game for you. If you like the constant stress of trying to keep things working then this is for you. If, on the other hand, you enjoy a far more laid back experience this almost certainly isn't. This is typified by the lack of help pop-ups you get in the game. The developers have done this on purpose, expecting you to constantly check with your advisors on what area to focus on next. The advisor tab offers you detailed advice about which area of the city is currently struggling. The game isn't designed to be relaxing - you're in charge of the city and it's bloody hard work.
This leads me on some of the negative experiences I had whilst playing the game. Placing buildings can sometimes be a bit of a pain – you can't rotate the building particularly easily and you'll sometimes struggle placing a building in a fairly crowded city.
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On my signal... Unleash hell!
One area of the game I haven't mentioned so far is the military aspect. In Caesar IV you sometimes face enemy forces - either barbarians hoping to rape and pillage or Roman forces, sent by the senate, tasked with removing you from office. Thankfully, there are a few ways of defending yourself.
To start with you can build a wall, fitted with a gate house, to encompass your city. Building this wall can be a frustrating and expensive experience. To start with you probably only want to protect the most important parts of your city, those being your people's homes. However, you can't build a wall where an aqueduct already exists. This leaves you with problems in getting water to your precious little people, without also leaving a hole in your defensive setup. I couldn't work a way round this one, which was frustrating.
Of course, walls alone won't hold any invaders worth their salt, so you can also supplement them with various groups of military forces. This too, is not a cheap deal and to build up a small armed force will cost a fair few denarii. Once established they tend to be a pretty well trained and effective outfit, provided you have the industrial infrastructure to create weapons for them. I preferred the economy side to the game, finding it more fun operating trade routes and resource management, but the military aspect does offer a different angle.