Wait. Do you think that schedule and plan have only 1 definition and they are synonymous? Here, let me clear that up for you.
When you use Plan as a noun, it means to have a detailed proposal on how to do something. When you use Plan as a verb, it means to decide or arrange in advance. The verb form of Plan is synonymous with schedule.
However, I am using it in the noun form. Specifically, people can and do create detailed proposals on what to do for public health, how to harvest and distribute various crops/produce for food. How a city will allocate land for buildings, where to layout infrastructure like plumbing and power, and all sorts of health crisis. You can even create a plan for when accidents happen.
Hopefully, that clears things up for you.