To have a somewhat imersive experience in Dual Universe we definitely need to see cities. But why exactly would people create cities in DU if just use a vast amount of resources without any real benefit except for showing off?
Normally city planning depends on a lot of different factors, like the environment, available resources, especially food, the condition of the ground, expected industries etc. Those are mostly things that wont work in DU. On the other hand, building cities in DU has quite a lot of disadvantages, like being target for raiders, warmongers or just griefplayers. So without any real benefit or need to create cities we will at most have very few large organization building and maintaining a city as HQ and maybe one or two trading hubs. Mostly we'll see well hidden factories and bases which are statistically placed across the planets with nearly no clustering.
There are two possible ways to facilitate cities. One is giving artificial benefits like production bonus or similar things, i wont advocate that as it is unrealistic and just shows a lack of creativity in the game design. The second way is giving realistic incentives. The only incentives that work on larger scales in a mmorpg are economic or security benefits or needs. Social or educational facilities can be mostly ignored (there could be University-Type elements that increase the speed of accumulating xp for the first 20% or something of the skilltree, with which organizations can cater to new players, but that wont be a real incentive for creating a city).
In my mind there are three mechanics which would directly create the need for clustering buildings on a small area:
1. Powergrid
The first suggestion is, that all functional elements (Doors, electronics etc.) require electricity. Standard, small sized elements would need a marginal amount of power so, that a small generator that can easily be installed in every ship/building is sufficient to support them. More advanced facilities like factories, Elements with strong supporting effects (something like the University for example, or greenhouses), military elements (planetary turrets, shields, sensor units ...) however should have an exponential increase of the power required. Factory units for example should require enough power, that no stacking of small generators can support them.
To support those power hungry elements players can build power plant elements which are extremely large on scale, like 64³m³. They would support buildings within a certain radius with a set amount of power and to increase that radius you could create power-relay stations. What does this do for city building? If players want to run a factory or other facilities they need to create a power plant. If a single power plant generates enough electricity to support several factories, then the economic way of action would be creating enough factories within the vicinity of a power plant to effectively use the generated power. A large cluster of factories in turn needs military protection as it is a nice target for raiders, thus we have some kind of city growth. At the same time owners of those power plants could rent space in the effective radius for players which can afford to create a factory, but not the required power plant.
This can be extended to every kind of large scale element which would be nice to have in a city, for example if we want a space port in the city. The simplest way would be to just create some flat areas for ships to land on. But what about quality of life services like refuelling or rearing constructs? Those actions can take ages. If we had large scale elements like a repair Dock, which repairs damaged ships in the vicinity if activated or refuelling stations, those can save a lot of time to players. Elements like that would also require a lot of power, thus the need for a power plant in the vicinity.
In short, if every advanced element has a big size and a large power requirement, coupled with the need of power plants, we would by default see clusters of buildings which can be called cities.
2. Resources
We can see in some videos how the ground is removed with a tool, its fast, efficient and effortless. if we can mine resources in this way, then DU players will be like a big locust swarm, run across the surface of a planet, scanning and within hours mining all interesting resources. But a big influence on city-building is the need to create a permanent structure in specific places, thus mining resources should definitely not be near-instant. Optimally mining out a big underground ore vein should take years if done by hand or several months when done with elements for mining. If we have long term mining then locations get a certain economic and strategic importance. If an organization finds a large vein of a rare metal it can't just mine it and go away, it has to defend this place against other players. Thus they need to create defensive structures, which again need power plants. If you have defensive structures and power plants on a mining base and some power surplus due to it then its economic to just continue and create the needed refinery elements etc. too, which in turn leads to clusters of buildings again.
3. Dependencies
Similar as all functional elements require electricity there can be other dependencies which make it necessary to create several constructs at the same place. In the new content update we learn about market Bots, where resources can be sold for quanta and elements can be bought (probably very limited after crafting is implemented, but maybe some of the most basic elements can still be bought). Those Quanta and elements aren't created from void and the sold resources can't spontaneously vanish. So if someone wants to place market bots in his base, it would make sense to require a trading hub element in the vicinity. There are quite some heavy industries which are dependent on water as coolant, so some refinery elements could actually need water purification plants in the area, the same plants could be used to support greenhouses or other buildings with water. If several buildings depend on each other there is a huge potential to incline people to gather together and create cities. Especially as everyone has a limited amount of cores available.
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I really think that those three points are absolutely necessary for a good experience in DU and will lead to some pretty interesting results.
