Buffer Requirement. No medical marijuana use shall be located within one thousand (1,000) feet of then existing elementary or secondary schools, licensed child care centers, or churches, except when the aforementioned uses establish themselves within the prohibited distance, the medical marijuana facilities may remain. Measurements shall be made in a straight line, without regard to intervening structures, from the nearest point on the exterior building wall of the school, child care center, or church, to the nearest exterior building wall of the building containing the medical marijuana use or the property line of an outdoor medical marijuana cultivation facility.