Reading assignment. This paper is the second in a continuing series of papers designed to enhance the reader?s modeling skills. Modeling Exercises Section 2 contains two separate modeling exercises. In the first exercise the reader will build a system dynamics model based on a detailed description of an urban system. The reader will run the urban model under varying conditions. The second exercise asks the reader to perform mental simulations on a pre-built model, and to estimate the model behavior under different conditions. The reader is expected to have prior experience with system dynamics, model building, and mental simulation.