I found this article about city shapes
and just ... had to laugh. "Only" is a dangerous word.
Off the top of my head, I can think of at least three other city shapes: hexagonal, radial, and vertical.
Now hexagonal was never common, so I'm not surprised they didn't include it. It's super efficient for space but not very convenient for traffic, and humans figured that out fairly fast. But I did find a hexagonal example
on a search.
Radial is a spiderweb, with straight crosslines and straight or curved perimeter lines around a focal point. You see it in cities butted against an edge like a lake or mountain, or cities that grow up around a central point like a castle. Here's a nice one with concentric circles
, and a bigger one done all in straight lines
. This huge one is a bit more gridlike
, but you can still follow the pattern of radial and perimeter lines.
Vertical cities go up the side of a mountain or cliff, such as pueblos. Sometimes they have a vertical grid if they are built, other times a more organic pattern if they are stuffed into whatever holes
people can find already there. This cliff city
basically has a front (the air) and a back (the cliff) and its access ways are mostly stairs and ladders
instead of streets. This mountain city
seems to have a central access for boats
and most of the rest is tall buildings jammed right next to each other. Once again the prevailing direction is up/down and the primary transit is probably stairs, as it looks older and poorer than the kind of city that puts an elevator in every building.
And of course, not everyone cares about efficiency. Here's one based on circles
with houses in wedges, which totally do not pack well. This one uses ovals around each house
. Very retro, that's what got people trying hexes and later square grids. But if you want
that green space in between housing clusters, suddenly these models make a lot more sense.
Another division is between manmade and organic. Grids are manmade, using straight lines and regular patterns
. Organic shapes are more random and curvilinear, like some subdivisions, and rarely work as well. (See Stupid Street Design
and Stupid Lot Shapes
.) In the article, the grids are over-represented in their set of four, and curvilinear shapes -- which do exist -- only somewhat.
Then there's the question of navigation. Modern cities are pretty much built to be easily navigated. They want people to get in and out and around them easily. This was not always so. Once upon a time, cities were sometimes built for defense so that the streets were either a completely chaotic maze, or later on, deliberately designed to slow progress from the rim to the center. It's how you discouraged invaders. You got a similar effect if people just built stuff wherever they felt like it and/or followed natural features such as rivers. Then the Romans popularized the grid. Rome! By firelight! <3 You could charge an army right down those streets on a straight run. For centuries, in fact, barbarian hordes had great fun doing that. Here's a fascinating comparison
of which cities have a regular grid and which are tangled.
Come on, math dudes, get your heads out of your cultural bias.