I am wondering what the set of differential equations is that is used to model how viruses spread in a population?
I am also wondering how epidemiologists get around the highly irregular shape of a country to make more-or-less accurate predictions.
There seem to be a couple possible approaches that come to mind, one being a partial differential model based on density and time over a spatial distribution, but as well a system of several ordinary differential equations that resemble logistical modeling.
The most likely set of equations seems to be something pertaining to what is mentioned here
but this also mentions logistical-appearing variants.
I have seen others related to reaction-diffusion and second-order partial differential models.