Scatter cities have overlapping buildings and roads that are scattered randomly, with some control on where they have higher probability to appear, and on their size. These cities are simpler, lighter, and faster to make, but less precise, best for far-away shots.
Here you'll learn how to create one as quickly as possible. In the detailed page, you'll see more details how the generation works, so you can adapt it to your own needs.
Start by importing the pre-made assets and preset city graphs, as explained in the fundamentals.
In the outliner, only leave the SC low-poly city object visible. This object and its data are always appended, not linked, so that it's easier to manipulate and modify if needed. The city will be a single mesh, and it'll be that mesh in that object.
The SceneCity low-poly assets collection is necessary also, this is where you'll find a low-poly building and low-poly road portion.
However the other imported collections are unnecessary in this example, so you can delete them. To do that, right-click on them, delete hierarchy.
Select the scatter city preset graph, in SceneCity's node panel. Then locate the node in this image (middle right of the graph) and click on its button. It will generate and update the city mesh, and you'll see it in the viewport. The mesh object was already present in the scene before, but its mesh was empty. So now that SceneCity has updated it, it is visible.
What you just did is tell SceneCity to scatter two different types of buildings (procedural cubes, and a custom mesh) over a given area, according to a distribution and size map. They are output as a single merged mesh.
Locate the graph node in the image above (top right of the graph) and click on its button. Then in the viewport choose the shaded display mode (named lookdev in 2.80). Select the city, and apply the material SC low-poly building facade to the first slot. The second slot is for the roofs of the buildings, but we can leave it empty for now.
What you just did is tell SceneCity to create / update an image datablock (so within Blender, not an image file), to be used in a pre-made material that was appended from the library along with the city mesh and object.
In the outliner, select a collection for the roads, or create a new one.
At the bottom of the city graph, click on the two buttons in the image, in that order. The first one creates curves for the roads, the second one adds the road portion object along those curves. You could also manually add a ground plane for the city.
Notice how the roads flow nicely in the city, and have different heights also. However they overlap, and never branch.
Now you have a basic understanding of how scatter cities are made. You can try and experiment with the graph, see if you can figure things out (play with the seeds for instance, to get different but same-looking cities), study how the buildings and roads are made, change the materials, or add manual details to the city.
Next you should learn how to create such cities from scratch, use them to their full potential, so they can perfectly fit your needs and your urban projects.