COMPUTATIONAL SOCIAL SCIENCE

GeoMason Examples


GeoMason has recently been updated to support changes to MASON itself and we have contributed a few  models to highlight the basic functionality of GeoMason and act as examples for how geographically explicit models can be built.

Below are some of the new models that now come with GeoMason.

Sillypeds

This model demonstrates how one can use GeoMason to explore evacuations from a building. The simulation starts by reading raster data describing a building layout (converted from CAD files). The simulation randomly places a number of agents on walkable areas within side of the building. Once the agents have been placed on the ground, they follow the lowest cost path to the exit (in this example there is only one). The movie below demonstrates how the agents (red dots) move through the space, and through this movement congestion emerges around the exit. The yellow paths are traces of pedestrian moment.

Water World

Inspired by NetLogo's Grand Canyon Model. The aim of the model is to show how data in the form of a elevation, can be used as a foundation of a simple spatial agent-based model. Similar to the Netlogo model, the elevation data comes from the National Elevation Dataset. It was converted from an ESRI Grid into an ASCII grid file using ArcGIS.
Similar to Sillypeds, the elevation data acts as our terrain, in this case its Crater Lake in Oregon. Agents within the model (in this case water) fall at random over the terrain and then flows downhill over the terrain. If the water cannot flow downhill, it pools up and once the gradient is sufficient, the water flows. For example, water falling in Crater Lake, initially has to pool up until the water level is sufficient to breach the caldera. Once this occurs water flows out of the lake as highlighted in the movie below.


In the second movie (below) highlights the testing of the inner logic of the model, in the sense are the raindrops doing as they are expected to do. If you want to test this, uncomment out (e.g. remove '//') from either one of the two lines below:

//landscape = setupLandscape(); // uniform landscape, completely flat

//landscape = setupLandscapeGradientIn(); // landscape that slopes in

These lines can be found in the start method of WaterWorld.java file but ensure you comment out the (e.g. add '//' ) to the following line:

landscape = setupLandscapeReadIn("elevation.txt"); // read landscape from file



GridLock

This basic traffic model explores how agents travel to Tyson's Corner, Virginia for work. The idea is that if you increased the number of agents (people) more congestion will arise. To some extent this is similar to the GeoMason sim.app.geo.campusworld example.The model demonstrates how you can make agents move along networks (in this case road lines in the form of ESRI shapefiles) from their origin to their destination via a shortest path algorithm. 
The number of agents is based census tract information i.e. the number of people who work in Tyson's Corner and their corresponding home locations which is restricted to Washington DC, Virginia and Maryland. The movie below shows the fully functional model.

 

Schelling Polygon

In this model we demonstrate how one can use polygons (such as census tracks) to create an abstract Schelling model stylized on Washington DC. The model reads in a ESRI Polygon shapefile and uses attributes of the shapefile to create Red and Blue agents and a number of Unoccupied areas. As with the traditional Schelling model, Red and Blue agents want to be located in neighborhoods were a certain percentage of their neighbors are of the same type. However, instead of using a Moore or Von Neumann which is common practice in cell based models. Here neighborhoods are calculated using the neighbors that share a common edge to the agent in question. If an agent is dissatisfied with its current neighborhood, it will move to a random Unoccupied polygon, regardless of whether or not this new location meets its preference. The movie below shows this movement.

Point Schelling Model

This model in a sense extends the Schelling Polygon model, however, instead of the polygon being the agent we take attribute data from the polygon model and create individual agents (see Crooks, 2010). This is based on the notion that much of the data we have comes at an aggregate level and often in some sort of vector representation of space such as census data. However, if we want to model the individuals or groups of individuals, we need to disaggregate the data.
To do this we create a number of Red and Blue agents based on population counts held within the polygon shapefile. As with the previous model, all agents want to be located in neighborhoods were a certain percentage of their neighbors are of the same type. However, instead of using a Moore or Von Neumann which is common practice in cell based models. Here neighborhoods are calculated using buffer distance from the agent in question. If an agent is dissatisfied with its current neighborhood, it will move to a random location, regardless of whether or not this new location meets its preference. Moreover, the model demonstrates how to link points (agents) to polygons along with some other basic geographical operations (such as union, point in polygon, buffer). The movie below shows this movement both at the individual level and at the aggregate (census track level).


 

SLEUTH: Urban Growth Model

This model shows a basic urban growth model based loosely on the SLEUTH model. In the sense, that we have only implemented the four growth rules (spontaneous, new spreading centers, edge and road-influenced growth) and not the self modification element of the SLUETH model. The model demonstrates how different layers (e.g. slope, land use, exclusion, urban extent - urbanized or non-urbanized, transportation, hillshade) can be read into a model to provide cells with multiple values. The movie below shows a specific growth scenario under specific coefficients (parameters) for Santa Fe, New Mexico.


More information about GeoMason can be found here along with the source code and data for all the models presented in this post.

Click here to see more models