For both primary and computed attributes, the attribute to be used as an indicator can be identified by its fully-qualified name, for example:
Of these, urbansim.gridcell.residential_units is a primary attribute -- the number of residential units is part of the data stored for each gridcell. Population is computed, even for gridcells; for a gridcell, it is computed by summing the number of persons in each household located in that grid cell.
Attributes can also be in project-specific packages in
addition to ones in the urbansim package. For example, in our
PSRC application of UrbanSim, one of the indicators
is
psrc.zone.travel_time_hbw_am_drive_alone_to_cbd, for the
zone geography defined for this application.
As with other Opus variables, the variable name for variables used as indicators can be a template that matches a family of related variables, such as psrc.houeshold.has_DDD_cars. This variable can then be instantiated with a particular number of cars, e.g. psrc.houeshold.has_2_cars.