It's done by a model. There are various kinds of flood plain mapping.
On one hand, the Insurance Bureau of Canada will talk about the flood plain mapping that they do. It's a very high-level mapping that takes a picture. That doesn't give you the granularity that you would see in flood plain mapping that municipalities or provinces are doing right now, as an example, with some of the funding they're getting through the natural disaster mitigation program.
There's high-level flood plain mapping that gives you a snapshot or a picture, and then there's flood plain mapping that's very technical and detailed.