Geographic migration

Human migration is a important factor in the spread of disease across a geographic region. EMOD represents geography using nodes. Migration occurs when individuals move from one node to another; disease transmission occurs within nodes. Nodes are very flexible and can represent everything from individual households to entire countries or anything in between.

Therefore, to include migration in a simulation, you must define multiple nodes. At each time step (usually one day), each individual has a defined probability of migrating out of their current node to another. If they migrate, they can then acquire or shed an infection in that node. The mode of migration can be local (foot travel), regional (roadway or rail), air, or sea. You can also define different migration patterns, such as one-way or roundtrip. For more detailed information, see Migration parameters.

For STIs including HIV, you can specify the consequence of migration on an individual’s existing relationship. For example, you may configure the simulation such that an individual’s partner will migrate with them for marital relationships, but the relationship will be terminated for informal relationships.

You must include a separate migration file for each mode of travel that describes the migration patterns for each node. It lists the migration rate for each node. Migration rate is defined as the fraction of the node’s population that is migrating out of the node per day. Units are per person per day, meaning the number of people migrating per day divided by the total population of the node. For more information on the structure of these files, see Migration files.

The Generic/Zoonosis scenario in the downloadable EMODScenarios folder includes daily migration. Review the README files there for more information.