I'm trying to create more opportunities for roleplay in a setting where most civilized cities are along the coastline of a "new world." Most cities are fortress cities on the frontier that serves to protect other colonies. Since most of my cities have the same constraints (protection, etc), there is a risk that they'll all look basically the same.
How can I design these cities so that they have more variation, so that each city is interesting and individual? What process will help me do that?
City design can be broken down pretty effectively. These are some options (certainly not an exhaustive list.
Source: What is the city's history? Why did it form? EDIT: And when! This is crucial to deciding the history and evolution of a city (obviously) There are a few options here.
Evolution: How does the city evolve from its source?
Result: Now you can mix and match to your liking. Lets say a natural resource node is found. The closest authority (city-state, nation, empire, etc) decides to create a fort to control the node as well as incentivizing or forcing citizens to go collect the resource. At the same time, entrepreneurial citizens move that direction to capitalize on the new population building up inns and pubs, blacksmiths and so on. So in this scenario you have three sources and you will have at least two if not more methods of evolution that mix and match.
One last point. Cities are a system non unlike a chemical reaction. If a new city suddenly pops up like in the scenario above that takes resources and manpower away from other cities. When you are a trying to create a realistic local environment, say the size of a county with a dozen population centers (or on an even larger scale), this is important to consider. It can also provide plot points for that matter. Maybe cities are fighting over a resource location or a holy site and they create cities or forts on opposing sides of a river... how will that develop?!
So this is truly a process and do not underestimate the value of a web of cities when creating a setting. Lastly, you really must have a city's history in mind, (or create it as you go when picking from the lists).
Enjoy.
When I can, I like to do it in historical layers, starting with the pre-settlement landscape, and then going through the place's history of development and major events. I at least like to have a sketch of what was there at a few points in the past, so I know when and why each area was built, and what each area may have had before its current state. It makes the final state make more sense and be easier to hold in mind and work with, for me, when there is an actual history and not just a final state. It also helps me have an idea how the city is currently developing, and what is going on there.
One example of how this can be nice, is houses of prominent people. Instead of just declaring a rich neighborhood where fancy houses are, I might have noted where the people in charge of the shipyards during an early stage would have built their houses, and so on, so notable houses and buildings with history refer to actual people from a certain era, and are located in places that make sense within that history.
Another nice thing it creates is older industrial areas and older versions of municipal buildings that may have been replaced, or shifting road networks, etc.
Citys grow We don't need to discuss that, there are a few examples of planned citys but these are not the topic here.
So when we assume that your city is a grown one, the question is how it is grown. There are various effects on the way a city grows and I want to cut the most important ones:
Economy
This aspect has multiple effects. Beside the speed, which is increased by good economy and decreased by a bad one, this also effects what kind of buildings raise and where they're locatet. For example, a miner-settlement will grow living houses beside the mines. As the settlement grows, some of the living houses will be used as shops and light crafting houses.
Later there will be workshops like smiths, butcher etc. Workshops which emit smell are likely to be build in a little distance to the town. Later other workshops of this kind settle beside the other smelling workshops and even later, as the city grows, there will be no more distance between the workshops and the living houses, so even if they smell, one day they might be surroundet by houses.
In my example, what happens when the coal, or whatever they're mining, is empty? Many workers will leave and the economy might collaps. But maybe they find another economy. The city might have some dacades very poor economy, thus some houses will be abondoned and colapse.
Terrain This is surely the most important point. If the city is build nearby a river, one day they will build an harbour and like any economic facillity the houses will grow toward the harbour. If there's a natural border like a cliff, they might cannot build on the other side of that border. But later hey might be able to.
Epoch As I already told, growing fastens and slowers ofer time, depending on the economy. This means that several buildings, which have the same purpose, are build in different epochs and look different. Best example for that is an old town. Also, over time some buildings collaps due bad maintenance, fire, whatever. These will be replaced when space get rare, thus there might be younger buildings in older parts of the city.
Current epoch has good economy or just came out of big destruction? There might be many buildings out of this epoch. Current epoch has bad economy? Maybe they build a few houses, maybe they altered existing houses,...
Disasters Epidemic, fire in "wood-only" parts of the city, earthquake and most destructive: war. These events often destroy wide parts of a town and kill many people. Depending on the political and economic situation this can be both, good and bad for the city in long term. For example, after WWII western germany managed become one of the leading economys in the world. Not really a city, but the issue should be the same. At the other hand, many citys get abondoned when they're destroyed (not talking about metropolises wich are rebuild in general). Disasters which destroy large parts of the city lead to the different buildings as I wrote at epoch.
None of these points are standing on their own. Every point is effecting the others! Epoch has a strong bounding to economy. There will unlikely be a good economy over long time if the terrain is bad (no mining, bad infrastructural connection, ...)
The most important point of citybuilding is:
Its art! Be creative and have fun! If you don't like it you surely manage someone else who does and will help you. If you are not happy with your outcame, show it to other people and ask them for helpful critic, this issue can't be handled with general tips.
There is great advice all over this page, so I'll just add two cents worth.
The landscape can make a huge difference between cities. If there is a mountain near the shore, a fortress could be set up backed against it with all of its armament pointed out to sea. An early warning watch tower could also be placed high up, and see danger approaching from further away. This could attract more seafaring trade because the port would be extremely secure. Other factors could be resource availability, natural coves or reefs, natural cave formations for secret entry/exit during a siege, a pass through a mountain range, leading to caravan travel, etc.
History has been mentioned, but here are a few other questions to ask. Was a war going on when this city was built? Was the city built as a fortress to begin with, or were fortifications added to an existing city? How does this influence its design? Perhaps a fire raged through a large portion of it and so a chunk is newer/more purposefully designed than the rest. Perhaps one of these cities is (or was) the capitol of the region. Edit: One other factor: Since there seems to be a war going on, maybe one of these fortifications could be a captured city. It used to belong to the enemy, and maybe a lot of its citizens are still loyal to them. Most likely their style of building, etc. is very different as well. Instead of star-shaped forts, they built hexagons, or the architecture is informed by a different military structure. Known for their mounted soldiers? A huge stable centrally located and large portcullis at every cardinal exit.
But most of all, one of the biggest things that makes a city seem different from any other is the notable NPCs living there. A brutal police force in one, a well-developed crime syndicate in another, a third where the tradesmen have unionized and basically run things. A particular noble philanthropist with a dark secret? Pride-of-the-nation citizens who keep the city clean and always have a "Good morrow" for passersby? A veteran commander turned smuggler in peace time? A well informed street urchin who can get places unnoticed? A master-of-the-'ouse inn-keep with his hands in everyone's pockets when they aren't all over the ladies? Sprinkle in characters like that, and your players will stop seeing the similarities between cities and start noticing all their differences.
Something that has not been mentioned yet is the raw materials that houses are built from. If the city is near a volcano, there will be mostly basaltic rock available, making the houses black/dark gray. If there is sandstone instead, houses will be more reddish. Limestone => white/light gray. If there are not much rocks available (mountains are far away), then houses will be made mostly from wood and clay.
If you look at cities, you will see that these things are mostly not mixed. There will be one prevalent "color" of houses.
There are some good answers here already, but I notice that there has so far been no mention of climate. This is a major factor in building design, where designers might have to cope with either high or low temperature, large volumes of rain or snow, storms from the coast, high winds etc. These can all have an influence on the design and layout of a city and can add flavour to them. For example a northerly town could have highly pitched roofs so that the snow does not accumulate, or a city that is in a very hot location might have buildings with thick whitewashed walls to keep them cool.
Working a city from the ground up can be tiring, but when I need to make a city, town, village etc quickly, I generally pick something that i'm going to need; say, a particular bit of scenery, the mansion where a ball is going on, the streets where a brawl is going down etc, and build the city out from that. Unless the players are going to explore every part of the town, you can save effort by conserving details to just the ones you'll need right now. It takes a lot of the effort out of the whole thing, and you can ensure your cities are differentiated because you just don't put the same scenery in every one.
Definitely think about the fact that the cities would have originated in different times, expanded at different rates, and had different raw materials available. The difference in timing allows for a significant amount of variation as the most practical solution to problems would change as tools are developed. Cities that expand slowly are more likely to be carefully planned and built to quality moreso than shantytowns that evolved into city. A desert city is more likely to have buildings that incorporate mudbricks and sandstone whereas a city near a forest is more likely to incorporate wood.
As a bit of added flavor consider climate variation. Climate varies as you travel along a coast. This leads to things like San Diego and Seattle architecture being different.
This seems like an unlikely setup. The full growth of a city requires a certain amount of security. A Fortress City on a border has defense requirements that stunt its full growth, as everything needs to fit in the walls all the time. A city deeper in, away from the border but connected by roads to several forts can grow faster at need and the populace can be more confident they won't all die.
It also seems odd that these border cities are also on the coast. This means there is no protected farmland to grow food for them. In reality you would have port cities on the coast, and smaller forts distributed inland to give a secure border for the land. There might, or might not be cities in the middle, depending.
Something that hasn't been mentioned yet: think of the city's part in the larger political landscape. You might, for instance, build on the idea of the warring city-states of early Italy, the single capital dominating a culture, or the artistic centre resisting the tyrannical capital.
How does the city maintain its power, its independence, how does it attract its trade?
The nice thing is that you can treat your cities as characters. This lets you take all the tricks you have for developing characters and letting characters interact, and apply them to cities. Think of your city as a dominant dictator, a free-wheeling artist, a crafty merchant and work from there. (These are pretty one-dimensional, you can take it further, of course.)
The choices you make can be reflected in the architecture, the monuments, the layout of the streets, the division into districts, etc. Try to look at existing cities, and see how their history and character has shaped their appearance.
Real world cities look different because
If cities all have the same geography, the same function, and are founded by the same people at the same time,
Roman forts are an example for such similarity, and American cities, most of which have been founded roughly at the same time, look very similar to each other, too.
Open culture recently pointed to "The Medieval City Plan Generator: A Fun Way to Create Your Own Imaginary Medieval Cities", a free online tool to create maps of would-be medieval cities. Depending on one's inclination the generated can be used directly or taken as a "random seed" for one own's design. For some applications the quality of the maps might be sufficient. Other than the lack of terrain features - with the exception of a coast line and a river - the maps look rather convincing to the casual viewer (which of course the crowd of WB.SE is not...).
As of writing this answer you're free to use the result of the generator:
You can use maps created by the generator as you like: copy, modify, include in your commercial rpg adventures etc. Attribution is appreciated, but not required.
Cities (Towns would fit your setting better I think) in roughly the same area will always look kinda the same. They will have the same building-materials and proably the same culture and overall architectural style. What makes the difference are geography wealth and landmarks.
Geography: One town may be cramped between a mountainside and a river. Another one may be a port-city and another one sits in a swamp and is mosquito-stricken for most of the year.(This won't make it look different but it will still give a different atmosphere to it)
Wealth: A rich town will have feature large buildings which will be highly decorated and well-kept, while a poor town is dominated by simpler buildings.
Landmarks: I think the most defining feature of a town is probably it's landmarks. Is there a mighty castle that overshadows it? Or has it a very high church tower that can be seen from far away? Or maybe one of your towns has a very large gatehouse. Or the warehouse of a rich merchant?. Why would a modern tourist visit that city
I lecture Urban Planning at university level and can attest that there are almost an invite variety of ways to develop a city over time, determined mainly by the urban planning (or lack thereof) culture - this actually has one of the major effects on how a city feels, develops over time, and affects density, transport systems / layouts, building typology and so much more.
Here is a diagram / comparative analysis (using a 'Figure Ground' Map) of different cities throughout our world today:
A figure ground map is useful to compare urban planning cultures as it distills information into built form only, allowing us to compare road sizes, geometry, orderliness etc.
From this you can see the following affects a cities physical features:
The analysis and study of cities is fascinating as they are emblems of our own culture - you can tell a lot just by looking at maps that give you an idea of how people live, what priorities they have, and how they interact - and so look at these factors can provide you with tools to create endless variety in the cities you describe.
