A style of drawing built from flowing curves, such as vines, scrolls, tendrils and rounded flower outlines, in contrast to the straight edges and angles of geometric design. It is the usual look of floral city and workshop rugs from Nain, Kashan, Tabriz and Isfahan, where curved lines and flowers are combined for a harmonious, fluid effect, while village and tribal rugs are mostly geometric and carry only some curvilinear flowers. Fine curves need a high knot density; with too few knots they look blurry or pixelated.
The number of knots per square inch of a hand-knotted rug (KPSI; 1 KPSI is about 15.5 knots per 10 x 10 cm), counted on the back with a ruler as knots per vertical inch times knots per horizontal inch, averaged over two or three areas. More knots give sharper detail and, all else equal, somewhat more durability and a higher price, but density alone does not grade quality: Heriz and Bijar are durable at low to medium counts, while floral curvilinear designs blur without enough knots. Rough figures: under about 80 for coarse tribal weaves such as Gabbeh and Qashqai, 120 to 225 for many village rugs, 300 to 700 for fine city rugs such as Nain and Isfahan, and 600 to 1,000 or more for pure silk Qum.