Geographic information systems (GIS) introduced her-e offer a source of information for problems with a geographic dimension, such as layout and environmental decision making. A mixed-integer linear-programming formulation of a chemical-plant layout problem was developed, and is presented along with an existing formulation. The effectiveness of these formulations is highly problem- and data-specific, and a combination of the two formulations can be derived that is more effective on certain problems than either formulation alone. The formulations are ineffective for some problems due to the highly redundant sear-ch space engendered by symmetries in the layout-symmetries that can be eliminated by a more careful analysis of the situation using location-specific information such as existing units and facilities geographic constraints, wind, elevation, and soil conditions. Different classes of such information can be captured from a GIS and represented within the mixed-integer linear-programming formulation. Two cases studies presented illustrate the formulations and the use of geographic information for chemical-plant layout.