Computing an Indicator

UrbanSim ``indicators'' are useful representations of dataset attributes. How these dataset attributes are displayed is specified by the user. In this example a Lorenz Curve is generated.

1. In your command window, make sure you are in the eugene\tools directory. Then type the following command to open a tool that will allow us to specify and then view an indicator:

   python create_indicator.py
   

2. In the ``Cache directory'' field, enter the location of the cache directory created by the simulation, e.g. C:\urbansim_cache\ run_2006_11_15_15_12. This will be a directory in the output directory you specified when starting the simulation.

3. Leave the ``Compare to another cache directory'' unchecked. This option lets you compare results from two different simulations.

4. Select ``Lorenz Curve'' from Type drop down menu. This automatically generates the Gini Coefficient as well.

5. In the ``Attribute'' field, enter:

   urbansim.gridcell.average_income
   

   This entry contains the ``Opus path'' for a variable that shows the average income within each gridcell. More specifically, this Opus path specifies the location of a Python file defining this gridcell : it is in the urbansim Opus package, is defined for the gridcell dataset, and is located in the Python file named average_income.py. You can find the file containing the urbansim package inside your workspace directory.

6. Leave the optional ``Name'' entry empty. If entered, it is used as the name for the created indicator (and also determines the filename of the resulting indicator). We'll let the program use the default name (``average_income'' in this case).

7. Type in ``gridcell'' in the ``Dataset'' entry. This is consistent with the attribute we're going to create indicator for.

8. Type in 1982 in the ``Year(s)'' entry. Leave the optional Scale entry as it is.

9. Press ``Run Request'' to generate this indicator.

10. The tool will then compute the indicators. When the ``View results'' button becomes active, it means the computation has finished. Press this button. A web browser will be launched and page loaded with a link to the requested indicator.

11. Click on the ``1982'' link to see the Lorenz curve. This simple plot was produced by matplotlib, a Python graphing and mapping package.

    See http://www.urbansim.org/wiki/external/index.php/Indicators for a partial list of indicators that are known to work on the Eugene-Springfield data. Interpreting the Lorenz Curve and Gini Coefficient is defined for non-aggregate variables.

12. Press ``Close'' to exit this tool.