when i did the i3D tutorial they had the assets and told me to set them to 0 and they magically aline with each other and i didnt have to click new terrain plus it came with a floor.
Now I am attempting to make a urban map so do i have to design the floor/ground or make it through create terrain( i know not the assets).
If i understand you right you have used assets that came with a tutorial before, and those formed a complete map already. Now youre trying to create a map with an urban setting from scratch and are wondering wether to create a terrain and then put your own assets onto it or not to use a terrain. I dont see a reason for using a terrain in an urban setting at all. Terrains are used for outdoor settings, where in nature you have bumpy grounds while in the city the streets are plain (usually^^). So use your favourite 3d-modelling app (e.g. Blender, if you need a free one) and create your city in it, then import the models to unity and put them together.