As is true for size, there are no abstract optimums for the shape of a parcel of land. Cartain shapes, particularly very narrow or irregular properties, will severely restrict the choice of possible building types and placement on the site. Parcels that are square or possess sufficient width for an arrangement of buildings in adequately spaced parallel rows permit a greater choice. In practice the minimum width of site is set either directly by zoning or indirectly by setback requirements from lot lines. The effects of adjoining property and activity often vary according to a site`s physical site, the greater the influence that adjacent buildings have on its supply of light and air. Conversely, the wider the site, the weaker the influence.