 Usually airlines do not publish seat maps for every aircraft, only for the larger aircraft and for the ones flying on frequent routes.When passengers complete an online booking, or check in online, they are often also presented with an aircraft seat map.However, this data is typically sourced from the original text-only seat maps on computer reservation systems such as Sabre, where the seat map is simply held as a two-dimensional array and as such can only display a grid of seats, as opposed to the more ingenious layouts now used in first and business class.