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 in one 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 by multiplying the knots along one inch of height by those along one inch of width, averaged over two or three areas. More knots give sharper detail, like a higher-resolution screen, 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. Figures run from under about 80 for coarse tribal weaves such as Gabbeh and Qashqai, through roughly 120 to 225 for many village rugs and 300 to 700 for fine city rugs such as Nain and Isfahan, to 600 to 1,000 or more for pure silk Qum.