A real estate multiple listing service $($MLS ${?}^{***})$ system is which of the following?

$(1)$ A measurement of the elevation above sea level

$(2)$ A system used to track the zoning on real estate in a county

$(3)$ A system used to display demographic data linked to geographical locator data

$(4)$ A system that salespeople use to distribute, publish, and advertise properties for sale and sometimes to compile sales data on properties after sales occur