Real world cities look different because
- they are located in different geographies
- serve different functions
- where founded at different times
If cities all have the same geography, the same function, and are founded by the same people at the same time,
###they will all look the same
they will all look the same
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.