I heard that random gen is going to be worked on for alpha 20, and I'd like to point out something that I've noticed after looking at map previews for hundreds of seeds (literally -- check
https://docs.google.com/spreadsheets/d/1E1abSNz0_rsoDd-3AVp6SzxY-AF7eVjMfVNhIXN3X20/edit#gid=997179930 for a list of the seeds I generated on b180 alone).
There's a subtle issue impacting the quality of cities in random gen: a disconnect between block sizes and prefab dimensions.
Let me explain that with images. Take the following city, which is about as big as they can be in alpha 19 stable:
The first thing to notice is how varied the size of each one is. Out of 356 prefabs, 195 do not share dimensions with any other prefab and 80 share it with only one other prefab. Only 38 prefabs share dimensions with more than four others. Note that this isn't about the size of building themselves, but about the "plot" the occupy, including green area.
More importantly, the dimensions of the prefabs do not take into account the actual available space inside a city. In alpha 19 stable each block is 120x120 of usable space unless a road is missing. The space between any two prefabs is 8m, so optimal non-wilderness prefab sizes are 24x24 and 56x56, but there's only one prefab with the first dimension and none with the second. On the other hand, the size shared by most prefabs is 25x25, which inevitably causes empty spaces.
In the case of downtown prefabs, it is even worse. Downtown is
at most four blocks in size, but the skyscrapers, which are downtown-only, all exceed 56m in at least one dimension, as you can see here:
The Crack a Book is the only one of them that could fit side-by-side with another one equal to it.
Regardless, the disregard for optimal prefab sizes for cities result in a lot of empty space, like the industrial area of that city:
Unless random gen is made to make roads fit prefab placement, one of the most important things to improve random gen cities is to make prefab dimensions and block sizes a better fit for each other.
PS: I'm only talking about x and z dimensions, not y. Height isn't relevant here. I also sorted x and z before making these statistics, so x,?,z was considered the same size as z,??,x.