Everything on the island hangs off two harbors. Old Harbor, on the east side, is where the ferries land and where the hotels, bars, and shops cluster — if someone says "in town," they mean here. New Harbor sits on the Great Salt Pond, the big protected water in the island's middle, and belongs to the boats.
South of town the land climbs to the bluffs and the Southeast Light. North of town, Corn Neck Road runs one flat-ish, bikeable line to Sandy Point and the North Light. That's the whole geography — you genuinely cannot get lost for more than ten minutes.