Boundary Conditions simulate community populations entering or exiting a study area at user defined locations along the study area boundary. They can be used to mimic migration or other mobile behavior that results in communities moving into or out of a region. Examples of this include birds passing through a study area for seasonal migration and deer traveling into a study area located at a lower elevation to seek warmer temperatures during winter.
Boundary Conditions are managed from within the Layouts interface. They exist as a layer group within the Study Area layer of the Layer Selection pane. Creating boundary conditions requires creating a boundary condition set and then adding spans to the set by drawing linear features in the map window.
After a span has been drawn, properties for the span must be defined that specify the direction of travel, the time series data to use for in-migration population counts and, optionally, the size values for in-migrants. Each span can have more than one configuration of these settings. This means, for example, that multiple communities can use the same span and multiple directions of travel can occur at a span.
Boundary condition spans are grouped for display in the map based on direction of travel, In, Out, or Undeclared. Global symbol properties can be set that will apply to all newly added boundary condition spans, or symbols can be customized within each boundary condition set.
During simulation, a community will move into a study area along an “In” span according to the time series data configured for the span. No attraction layer is required for in-migration. Simulating movement out of the study area at an “Out” span requires an attraction source to pull community members out. An example of this would be an instinctual attraction drawing a community towards a geographic point or areal location. Any migration behavior can be animated in the simulation window and reviewed in output data tables reflecting community count, density, and size. Figure shows an in span (#1, purple) and out span (#2, green) and an undeclared span (#3, orange).
Figure. Boundary conditions manage the flow of communities into and out of the study area
Boundary Conditions are created and managed in the Layouts interface through the Boundary Conditions layer node. This is located within the Study Area layer located in the Layer Selection tab. Expanding the Boundary Conditions node in a new project will reveal the global directional layer nodes In, Out and Undeclared used for defining global symbols definitions. Once new boundary condition sets are created, they will appear below the global directional layers.