We improve in this paper the localization accuracy of visual SLAM (VSLAM) / GPS fusion in dense urban area by using 3D building models provided by Geographic Information System (GIS). GPS inaccuracies are corrected by comparison of the reconstruction resulting from the VSLAM / GPS fusion with 3D building models. These corrected GPS data are thereafter re-injected in the fusion process. Experimental results demonstrate the accuracy improvements achieved through our proposed solution.