Initializing a Population
STEM comes pre-built with human population data for most countries. However, this is not sufficient to model other populations such as animal populations. To do this, STEM provides a feature call "Population Initializers". A population initializer allows you to put a fixed number of individuals of a certain type in any region part of your model. You can create a new population initializer (select New->Population Initializer from the menu or click the icon of a man with an 'I' next to him in the toolbar). A wizard similar to the one below pops up allowing you to specify a name for your new population initializer and then select from the drop down one of the available options. The standard population initializer allows you to specify either an absolute number of individuals or use a population density (individuals per square km). Next, you also need to specify a population identifier, e.g. 'anopheles'. If you specify 'human', the population initializer will overwrite any existing human population data in a region.
Finally, you have the option to select a location where the population will be put. If you do not select a location, every region part of your model will be initialized with the new population. If you do specify a location, population will be initialized at that location only or (if the region is a parent region containing sub-regions) all sub-regions it contains. The standard population initializer sets the initial population to zero in all regions that does not match the location specified. However, if you have more than one population initializer in your scenario care is taken to ensure they do not overwrite each other's values.
The new population initializer will show up under the "Decorators" folder in the Project explorer. You can drag the population initializer into a new model. Hierarchically, population initializers are typically deepest in the model tree since they are needed by both population models, disease models, and infectors/inoculators.