Originally Posted by
Dimitri Harvalias
You can still use Revit as your authoring tools for individual buildings but it's not really meant to be used as an urban planning and visualization tool.
You might want to try exporting to Navisworks and creating an aggregate model there. The model size and the graphics engine in Navis can handle larger models much better than Revit can and navigating around the model is easier and quicker in Navis as well.
If memory serves one of the sample files that comes with Navis is the entire city of Bath in England that contains pretty much every building in the city. Navigation is smooth and easy for flythroughs and walking.