https://www.cdc.gov/nceh/casper/default.htm#:~:text=The%20Community%20Assessment%20for%20Public%20Health%20Emergency%20Response,It%20is%20quick%2C%20reliable%2C%20relatively%20inexpensive%2C%20and%20flexible.

They can plug in what data they want to pull up and it will pop up like this:

If they want to know how many people living in such and such an area has heart disease (that they've collected over the years of known cases) the arrow will point to those houses in that area, same can be done for vaccines, childhood vaccines, diabetes, the handicapped who may need assistance during an emergency, they can make it be anything they want to surveil it to be.