UrbanSim is an open source software platform for agent-based geospatial simulation, focusing on the spatial dynamics of urban development.  Since its creation UrbanSim has been used in the official planning processes for at least a dozen regional governments which were used to help allocate billions of dollars in regional investments in transportation infrastructure.UrbanSim was first conceptualized in the late 1990′s and implemented using the Java programming language. The technology landscape for scientific computing changed dramatically after that, and by 2005 UrbanSim was converted to Python, making heavy use of Numpy to vectorize calculations. By 2014, it became clear that UrbanSim should be reimplemented again to take advantage of significant advances in the libraries available for scientific Python. The new version of UrbanSim, called UrbanSim2, makes extensive use of community-supported scientific Python libraries to reduce the amount of domain-specific customized code to a minimum.UrbanSim is an excellent case study for the power of leveraging thework of the scientific programming community as scaffolding for adomain-specific application, as opposed to building an extensive customized solution in each domain. Additionally, the open and participatory nature inherent in nearly all of the open source projects described here has been particularly embraced by governments, who are often reticent to support large commercial institutions and balkanized and private data formats and software tools.
