Currently this is the largest MLS in North America, and it has evolved from a county-based system controlled by individual Associations of Realtors operating as members of and under the rules of the National Association of Realtors. By the early 1990s it became apparent that a sophisticated computer-based system was necessary to integrate the MLS systems of the many counties and jurisdictions in the tri-state areas (or, at least, tri-jurisdictions) of Maryland, Washington, DC and Virginia, most of which were in close proximity to the capital.