  Large-scale pre-training has shown promising results on the
vision-and-language navigation (VLN) task. However, most existing pre-training
methods employ discrete panoramas to learn visual-textual associations. This
requires the model to implicitly correlate incomplete, duplicate observations
within the panoramas, which may impair an agent's spatial understanding. Thus,
we propose a new map-based pre-training paradigm that is spatial-aware for use
in VLN. Concretely, we build a local metric map to explicitly aggregate
incomplete observations and remove duplicates, while modeling navigation
dependency in a global topological map. This hybrid design can balance the
demand of VLN for both short-term reasoning and long-term planning. Then, based
on the hybrid map, we devise a pre-training framework to learn a multimodal map
representation, which enhances spatial-aware cross-modal reasoning thereby
facilitating the language-guided navigation goal. Extensive experiments
demonstrate the effectiveness of the map-based pre-training route for VLN, and
the proposed method achieves state-of-the-art on four VLN benchmarks.
