This paper proposes Map-Assisted Planning (MAP), a novel framework that enhances driving planning by leveraging online mapping modules in end-to-end autonomous driving. MAP explicitly integrates segmentation-based map features and the current vehicle state through a planning-enhancing online mapping module, a vehicle state-derived planning module, and a current vehicle state-based weight adapter. Experimental results on the DAIR-V2X-seq-SPD dataset demonstrate that MAP achieves a 16.6% reduction in L2 displacement error, a 56.2% reduction in road deviation rate, and a 44.5% improvement in overall score compared to the UniV2X baseline. Furthermore, MAP ranked first in the End-to-End Autonomous Driving through V2X Cooperation Challenge Track 2 of the CVPR2025 MEIS workshop without any post-processing. This demonstrates the effectiveness of explicitly leveraging semantic map features for planning and suggests a new direction for improving the architectural design of end-to-end autonomous driving systems.