City Engine is a powerful software package and forms part of the ESRI suite of GIS software packages. The power in City Engine is that everything is built using "rules" using Computer Generated Architecture. This allows for large developments, even entire cities, to be modelled quickly. It doesn't end there though as the software allows scenarios to be developed so that different development options can be reviewed, the model can be changed dynamically and other analysis carried out. 

In addition to using CGA models can also be created using Sketchup (or other similar software) and then imported into City Engine. There is a balance though between creating a model which can be used to deal with a specfic question, for example visual analysis and one which provides finite detail. Using CGA rules and creating simplistic block form layouts is often a case of "less is more" and are very useful at the Master Plan stage of a development. As projects develop more detail can be added and models created to be more realistic. 

Some time has therefore being spent of creating a library of Sketchup models which can be used for a variety of projects. CGA rule based models are also being developed and the advantage here is that parts of CGA rules can be used across a wide range of applications.