In the cities of this type, the roads are restricted to parallel and perpendicular directions, and the buildings and the roads never overlap. They are perfectly assembled, a bit like Lego blocks. You have control on how many districts types you want, and which buildings to use for each district type.
Here you'll learn how to create one as quickly as possible. In the detailed page, you'll see more details on how the generation works, so you can adapt it to your own needs.
Start by linking or appending the pre-made assets and preset city graphs, as explained in the fundamentals.
In the outliner, delete all the collections, except for the high-poly assets, and the high-poly asset instances collections. (To delete a collection, right-click on it -> delete hierarchy. If you linked the assets instead of appending them, to delete a child collection, first make the parent collection local by rick-clicking on it -> ID Data -> make local)
Those assets will be used by the city, they will be instanciated. Keep the collections disabled, to keep your viewport clean and uncluttered.
Create a new collection, name it City, then select it to make it active in the outliner. The city and all its objects will be created into the active collection.
In SceneCity's node panel, select the grid city preset graph. Locate the node in this image (right of the graph) and click on its create button.
What you just did is tell SceneCity to instantiate the roads and buildings models, according to a random district map. They are output as dupli vert instances, meaning they're very light. It's also possible to output them as individual objects, but they're heavier for Blender to handle, so you'll be a lot more limited in how many you can generate.
You can easily delete all of them with the delete button, provided you did not rename the generated objects, nor change the prefix text field on the node, because that's how the objects to delete are found: by name prefix.
You can easily change the city size by changing the value of the grid size, to something larger. A grid cell is 10 by 10 meters by default, and the pre-made assets are also modeled to that scale, so you cannot change the cell size without changing the assets too.
Don't make the grid size too large or it will be very long to generate, and Blender's viewport will lag.
You can also easily have a new random district distribution by changing the layout's seed. Click on the randomize seed button, then delete the old city by clicking on the delete objects button of the previous node above, then click create objects again.
Now you have a basic understanding of how grid cities are made. You can try and experiment with the graph, see if you can figure things out, 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.