Unity3D large maps advice - How big is too big?
Using the Unity3D engine. I'm making a multiplayer game for fun, using Unity's standard networking. If servers hold 25-50 players, what map size is recommended? How big can I make a very detailed map before it is too big for effective gameplay? How do I optimize a large map? Any ideas and advice would be great, I just want to learn and could not find anything about this on google :D
*My map is sliced into different parts.
Answer
The size of the map itself, in units, doesn't matter for performance at all. Just keep in mind that Unity (as any other game engine) uses floats for geometry, and when the float values get too high or too low, things can get funny.
What matters is the amount of data that your logic, networking and rendering engine have to churn through. These are different things, even logic/networking data, and limits on those greatly depend on architecture of your game.
Lets' talk about networking. There, two parameters are critical as your limits: bandwidth and latency. Bandwidth is how much data can you transfer, and latency is how fast. Ok, this explanation is confusing. Imagine a truck full of HDDs travelling from one city to another: it has gigantic bandwidth, and you can transfer entire data centers this way. But the latency, time for the signal to travel, is a few hours. On the other hand, two different people from these cities can hop on air balloons, look at each other in the night sky and turn their flashlights on and off. This way, they'll be able to exchange just one bit of information, but with the lowest possible latency: you can't get faster than light.
It also depends on how your networking works. RTS games, for example, often use lock-step multiplayer architecture can operate on thousands of units, but will only exchange a limited amount of data between users: their input commands. A first-person shooter, on the other hand, heavily relies on latency (which lock-stepping can damage): 10 ms when you jump and fire a rocket launcher are much more important than when you say your troops to attack. So, the networking logic is organised differently: every player's computer predicts what will happen, but the central server has authority on what actually happened. Of course, what I'm writing right now are just general examples of architectures that can be used; choosing the right way to do the networking is very difficult, but very interesting and creative task.
Now, logic itself. Actually, most of the gameplay logic used in modern games is relatively simple in terms of cpu requirements, unless it's physics or AI. Using physics in a multiplayer game is tricky enough on it's own, because of synchronisation problems (remember floats?); usually, the actual logic that can influence who wins and who loses is pretty simplified: level geometry is completely static, characters move using easy logic without real physical force, and the physics is usually limited just to collision detection. Of course, you see a lot of physical-based visual stuff: ragdolls of killed enemies falling down, rubble from explosion flying up; but these are typically de-synchronised between different computers and can't actually affect the gameplay itself.
And finally, rendering. Here, a lot of different constraints make place. To tell about them all, I would have to describe the whole rendering pipeline of Unity on different devices, and this is clearly out of scope of this question. Thankfully, there's another way! Instead of reasoning about this limit theoretically, just to a practical prototype. Put in different game assets in the scene, run it on target device and look how it performs. Adjust, repeat! These game assets can be completely ugly or irrelevant; however, they have to have the same technical properties as what you're going to use in the real game: number of polygons, sizes of textures, shaders, etc, etc. Let's say, for example, that you want to create a COD-like multiplayer shooter. To come up with your rendering requirements, just put in N environment models with N polygons each, using NxN textures, put in N characters with some skeleton animations with N bones, and also don't forget some fake logic that would emulate CPU-intenstive stuff so your perfomance measuring will be more realistic. Of course, it won't give you a final picture, but it'll be a good way to start, and it's great to do that before you start producing a lot of art assets.
Overall, game perfomance optimisation is a very broad and interesting theme, and it's impossible to give a precise answer to such a question.