A system and method for generating a seamless road network of a large geographical area includes a plurality of GPS probe traces extending across a geographical area. The probe traces are divided into sub-sets base on criteria, such as accuracy. A plurality of threads simultaneously employ the sub-sets traces to generate an independent network of the entire geographical area. The networks generated using sub-sets having a high accuracy are preferred over networks generating using sub-sets having a lower accuracy. The independent networks are combined to form a seamless networks of road segments.