Sewing lines for sewing pattern pieces combined to form a garment is determined automatically using placement information and a graph. The placement information indicates at least matching relationships between at least the subset of the pattern pieces and placement points of an avatar onto which the garment is draped. The graph includes nodes and segments. The nodes are located on outlines of the pattern pieces. Each of the segments indicating a directed connection between adj acent ones of the nodes. Matching edges of at least the subset of the pattern pieces is determined by the placement information as sewing lines for at least the subset of the pattern pieces using the graph.