Often, I find it fairer and safer to plot the practice’s market area using patients’ zip codes. A medical group usually can determine from its records that a small number of zip codes — say five to ten — capture an area from which 60 to 80 percent of its patients are drawn. Thus, listing those zip codes in the restrictive covenant can accurately reflect the group’s true market penetration. And when the group limits its prohibition to the most important zip codes, rather than trying to capture every last zip code from which any patient is drawn, it shows a reasonable attitude that goes a long way toward ensuring enforceability. It is perfectly appropriate to reflect these prohibited zip codes with a map attached to the contract. However, be sure that the contract makes clear that the prohibition is as defined in the text, and that the map is purely for the employee’s convenience.