Multisize Patched Spatial-Temporal Transformer Network for Short- and Long-Term Crowd Flow Prediction

The prediction of urban crowds is crucial not only to traffic management but also to studies on the city-level social phenomena, such as energy consumption, urban growth, city planning, and epidemic prevention. The challenges of accurately predicting crowd flow come from the non-linear spatial-temporal dependence of crowd flow data, periodic laws, such as daily and weekly periodicity, and external factors, such as weather and holidays. It is even more challenging for most existing short-term prediction models to make an accurate long-term prediction. In this paper, we propose a novel patched Transformer-based sequence-to-sequence model, called MultiSize Patched Spatial-Temporal Transformer Network (MSP-STTN), to incorporate rich and unified context modeling via a self-attention mechanism and global memory learning via a cross-attention mechanism for short- and long-term grid-based crowd flow prediction. In particular, a multisize patched spatial-temporal self-attention Transformer is designed to capture cross-space-time and cross-size contextual dependence of crowd data. The same structured cross-attention Transformer is developed to adaptively learn a global memory for long-term prediction in a responding-to-a-query style without error accumulation. In addition, a categorized space-time expectation is proposed as a unified regional encoding with temporal and external factors and is used as a base prediction for stable training. Furthermore, auxiliary tasks are introduced for promoting feature encoding and leveraging feature consistency to assist in the main prediction task. The experimental results reveal that MSP-STTN is competitive with the state of the art for one-step and multi-step short-term prediction within several hours and achieves practical long-term crowd flow prediction within one day on real-world grid-based crowd data sets TaxiBJ, BikeNYC, and CrowdDensityBJ. Our code and data are available at https://github.com/xieyulai/MSP-STTN .