A feature atlas used for a locus synthesis was proposed.After analyzing the features of kind and size of coupler curve in the coupler plane

the feature atlas of coupler curve is completed.A cusp curve

an osculating curve and a cave and convex boundary line divided the coupler plane into some portions

the feature is different in a different portion of coupler curve.The size feature is expressed with the parameter of outsides

such as L

W

J1

J2

and J

and the size feature of coupler curve on the coupler plane is summarized with the equal to curve of these parameters.It is efficacious when using the atlas for locus synthesis

and the locus of points at will in the coupler plane can be foreknowledge.