Large and/or complex facilities require demarcation between hazardous and nonhazardous areas. This is separate from an electrical Hazardous Area Classification which is determined by gasses that might be present. Hazardous areas might be areas where there is a lot of heat, chemicals, voltage, etc. Non-hazardous areas might be pipe lines, gathering or transportation lines.
The demarcation between these areas is called the plot limit or battery limit. The hazardous areas are called on-plot and the areas on the other side of the battery limit are called off-plot.