OK, so go to the path I'm taking through folders is this:
(Opening each successive sub-folder until you get to the text file)
Dwarf Fortress-->raw-->objects-->entity_human.txt
This is the file that helps humans generate their civilizations.
Scroll down to "[DEFAULT_SITE_TYPE:CITY]" - this allows DF to have humans make hamlets, towns ad cities where they do. You'll also find "[TOLERATES_SITE_TYPE:]" here, which allows them to play nice with other civs that build these instead. There's also the
[BUILDS_OUTDOOR_TOMBS]
[BUILDS_OUTDOOR_FORTIFICATIONS] just below, so that's all good too.
So that covers city building. But what about Roads and Walled Cities and Dungeons? OK, so scroll down a bit further and you'll come across:
[WORLD_CONSTRUCTION:WALL]
[WORLD_CONSTRUCTION:BRIDGE]
[WORLD_CONSTRUCTION:ROAD]
[ETHIC:KILL_ENTITY_MEMBER:JUSTIFIED_IF_GOOD_REASON]
The "[WORLD_CONSTRUCTION:]" things let DF know that they'll build these things during world-gen as well. They don't have to - Necros don't build roads or bridges, for instance, just "Towers". I'm not sure if these "WORLD_CONSTRUCTION" bits need to come just before the ETHIC lists, but that's how it is in the human raws, so I just assume that it's required in other race's raws as well.
OK, so lets get out of the human file and go to, lets say, the elven one "entity_elf.txt":
Change the "DEFAULT_SITE_TYPE:" to "CITY", then add in
[BUILDS_OUTDOOR_TOMBS]
[BUILDS_OUTDOOR_FORTIFICATIONS]
right after that. (So long as you'd like your elves to build tombs and fortresses of their very own.)
Scroll down to the ETHICS list and add
[WORLD_CONSTRUCTION:WALL]
[WORLD_CONSTRUCTION:BRIDGE]
[WORLD_CONSTRUCTION:ROAD]
just before them, like it was in the "human-entity" file.
Save and exit - viola! Now your elves will also have places you can visit in adventure mode, be invaded and ransacked and have markets selling elven crap in their elven towns. (Which are built pretty much identically to Human ones now, except for being infested with elves who are animal-freindly.)
Dwarves are handled in much the same way, but reside in the "entity_default.txt" file. Since dwarves are the only playable fortress-mode race in vanilla, that file's going to have much more stuff in it. Regardless, just change the entries in "DEFAULT_SITE_TYPE" and add in the TOMBS, FORTIFICATIONS, WALLS, BRIDGES, and ROADS in the same spots we did with the elves and your dwarves will now also be represented as hamlets, towns, tombs, ect... in World gen and in Adventurer mode. I've made this modification to all the races I gen worlds for anymore, which leads to this next bit:
LOTS of NPC reactions are generated using this method. With uninhibited number of sites and uninhibited pop cap, the game usually crashes after around 200 to 1,000 years (depending on Titan attacks and the like thinning out the world-wide population), because all of my RAM is used up and the simulation calls for more. So I'll either put a population cap to 200 (like a good sized Dwarf Fortress) and let them make as many sites as they like, or set a site cap to 20 per civ, but let the population grow as it will. The first option results in a more urbanized setting with hamlets and roads EVERYWHERE, but swathes of particularly savage or evil biomes left conspicuously bare of habitation, while the second option results in more wars and long stretches of "Golden" and "Twilight" Ages.
(I often gen 10k year worlds, just to see what histories unfold - after year 300 or so, most balance out to a Golden Age or domination by either elves or gobs because they don't die of old age.)