Keeping road network databases up-to-date is crucial to Geographical Information System (GIS) applications such as road networking. The vector road centerlines extracted from field surveys and satellite images are expensive and labor intensive with long updating processes. The GPS data crowd-sourced by public transportation users, provides an expanding source for enhancing road maps because of its rich spatial-temporal coverage and reasonable level of accuracy. The overall objective of this project is to implement an optimized methodology, which generates road centerline from GPS data obtained from taxis in Beijing without using any reference plans. Since the dataset used in this project has longer time intervals between trajectories compared to previous studies, the extracted road network on straight road segments are more accurate than the extracted road network on highway ramps in this project.