A tract is a unit of land that includes the Appalachian Trail within its boundary. One tract is connected to the next tract, and the next, and so on. The connected tracts define the A.T. corridor through Maine, from Katahdin to the Mahoosucs. The A.T. runs north-south inside the corridor boundary. Don't assume the corridor is always 1,000 feet wide.
Tracts vary in size and width.
NPS, BSP, BPL and others own the A.T. corridor in Maine. The Maine Appalachian Trail Club looks after the corridor lands and the trail. When the A.T. corridor was laid out across Maine, the tract and corridor sections did not coincide with trail maintenance sections. Some MATC designated corridor monitoring sections nearly coincide with trail maintenance sections, others don't. This is why there are 70 corridor monitoring sections and 90 trail maintenance sections on the A.T. in Maine.