Given the increasing importance of predicting spatiotemporal events such as wildfire, crime, and traffic congestion, existing methods are faced with the challenge of balancing timeliness and accuracy. Late predictions may result in tremendous economic costs and human life loss, while inaccurate predictions are likely to cause unnecessary public resources and social anxiety. Therefore, balancing accuracy and timeliness is essential in general spatiotemporal event prediction problems. In this paper, we propose an Early Spatiotemporal Graph Convolutional Network (ESTGCN)1to adaptively determine the optimal prediction time, which makes a tradeoff between prediction accuracy and timeliness and addresses two major questions: 1) How can we determine optimal prediction time points for different areas, taking into account their unique characteristics and conditions? 2) How can we minimize the propagation of prediction errors throughout the forecast timeline? Extensive experiments on two large-scale real-world datasets demonstrate that our proposed approaches can give an optimal prediction time in advance for each area and outperform all baselines in early spatiotemporal prediction tasks.

With the growing number of cars in cities, smart parking is gradually becoming a strategic issue in building a smart city. As the precondition in smart parking, accurate parking prediction can reduce the time drivers spend searching for parking spaces and relieve traffic congestion. Meanwhile, VANET and the Internet-of-things (IoT) are the key elements of the current intelligent transportation system. With the IoT devices based on VANET becoming more extensively employed, a large amount of parking data is generated every day, and various methods are proposed for parking prediction, therefore, it is time to systematically summarize the parking prediction issues and the state-of-the-art prediction methods. In this survey, we first provide a comprehensive review of the existing methods used for parking prediction ranging from conventional statistical methods to the latest graph neural network methods. Then, we classify a variety of parking problems such as parking availability prediction, parking behavior prediction, and parking demand prediction. We also compile all the evaluation metrics, open data, and open-source code of the surveyed literature. Finally, we present the challenges and future directions of the parking prediction technique. As far as we know, this is the first survey exploring parking prediction methods, which will be of interest to both researchers and practitioners engaging in intelligent transportation systems (ITS) and smart cities.

Many real-world ubiquitous applications, such as parking recommendations and air pollution monitoring, benefit significantly from accurate long-term spatio-temporal forecasting (LSTF). LSTF makes use of long-term dependency structure between the spatial and temporal domains, as well as the contextual information. Recent studies have revealed the potential of multi-graph neural networks (MGNNs) to improve prediction performance. However, existing MGNN methods do not work well when applied to LSTF due to several issues: the low level of generality, insufficient use of contextual information, and the imbalanced graph fusion approach. To address these issues, we construct new graph models to represent the contextual information of each node and exploit the long-term spatio-temporal data dependency structure. To aggregate the information across multiple graphs, we propose a new dynamic multi-graph fusion module to characterize the correlations of nodes within a graph and the nodes across graphs via the spatial attention and graph attention mechanisms. Furthermore, we introduce a trainable weight tensor to indicate the importance of each node in different graphs. Extensive experiments on two large-scale datasets demonstrate that our proposed approaches significantly improve the performance of existing graph neural network models in LSTF prediction tasks.

Accurate long-term predictions help governments make decisions and residents travel, which is essential for the development of smart cities. Fortunately, due to the deployment of low-cost sensors, a large amount of time-series data such as parking availability data and air quality data has been stored, which makes it possible for long-term predictions. Many state-of-the-art studies based on multiple graphs have shown excellent performance in long-term prediction tasks. However, few previous studies employ multiple attention mechanisms to their models based on multi-graphs and thus fail to comprehensively capture the dynamic spatio-temporal correlations as well as the inner relationships among graphs. To this end, we propose a spatio-temporal multi-attention multi-graph convolutional network (STM2CN) framework for long-term prediction. We applied four different graphs to mine the potential contextual relationships and employed three attention mechanisms to capture the multiple graph and spatio-temporal correlations. Experiments on two large-scale real-world datasets demonstrate that the proposed STM2CN framework outperformed the state-of-the-art baselines.

In smart cities, on-street parking space prediction is the key yet difficult point in smart parking system. However, conventional prediction methods generally neglect spatial and temporal dependencies and cannot predict long-term parking events accurately. To this end, we propose a parking space prediction scheme based on the spatial-temporal graph convolution networks (STGCN). We first consider the instantaneous status of the parking to calculate the on-street parking occupancy rate (POR). Then, based on the POR, we exploit a time convolution module and a graph convolution module to extract spatial and temporal dependencies of the parking spaces, respectively. Next, we design the parameters of the STGCN to predict the POR of all the parking spaces based on the spatial and temporal dependencies. Finally, based on the real-world data sets, we compare the proposed scheme with the benchmark models. The experimental results show that the proposed scheme has the best performance in predicting the POR.