A plan view (sometimes 'top view' or 'overhead view') looks straight down at the object from directly above. For gate work, the plan view is where you see the gate post centres, the swing arc of a swing gate, the runout direction of a sliding gate, the relationship of gate to driveway and to side panels.
Plan views are essential for site setout. The fabricator and the installer both work off the plan view to confirm post locations, hinge sides, latch sides, and approach directions before any concrete is poured.
CAD60's drawing pack includes a plan view as one of the standard sheets, with dimension lines for opening width, post setout, and gate panel position relative to the posts.