The metal lines on the cooking surface of a grill pan are called ridges, and they have more than one purpose. First, they help drain away grease during the cooking process. Just like an outdoor grill, the grease from your meat falls between the grills and away from the food. Unlike an outdoor grill, this grease collects around the edges of your pan rather than falling into the fire. The other purpose of your pan's ridges has to do with searing. The raised edges only come into contact with the meat at concentrated points, creating a unique striped pattern. This allows you to cook at higher heats, charring the meat in some places and leaving it untouched in others.