The scientific delineation of geographical boundary, which is the basic scientific issue of geography, reflects the cognitive level of the spatial variation of geographic objects from scientific abstraction and systematic analysis. From the perspective of earth system science, this paper first explicates the core issues of the basic concepts, scientific content and basic properties of geographical boundary. Based on the principles of scientificity and systematicness, the paper classifies geographical boundaries systematically according to the intrinsic mechanisms, extrinsic appearance and scientific attributes of geographical systems. This paper focuses on the analysis of the mathematical connotation and expression of geographical boundaries. In addition, it compares the characteristics and differences of traditional and modern methods for geographical boundary delineation. Finally, we construct the research framework of "geographical boundary model", which integrates the characteristics of qualitative, quantitative and positioning methods of geographical boundary. The research is expected to enrich the theory and method in geographical information science with the analysis of concept and method of geographical boundaries.

Geographic events, as a basic construct in geographic process description, have become a core content of geographic information system (GIS). Due to the limitation of acquiring human activity data, GIS modeling and analysis of geographic events has long been focused on the event-induced changes of geospatial objects and the interaction between the objects. However, in recent years, with the explosive growth of location-based service data and the rapid development of quantitative depiction of human activities, the impact of geographic events on human activities and online social participation in geographic events have aroused wide concern in many fields, which poses great challenges to the space-time cognition, modeling methods and analysis framework of geographic events. In this regard, this study discussed the conceptualization and categorization of geographic events in the context of big data, and then introduced the space-time semantics and graph-based data model for geographic events. The "node-edge" graph data structure is used to establish event ontology, the secondary or cascading events, the evolution process, and the "cause-effect" interaction. The spatiotemporal data mining approaches for geographical events were also summarized, which are limited to conventional event detection in "physical space". Integrating "virtual space" event discovery and propagation simulation ideas into data mining approaches is essential for recognizing multi-scale spatiotemporal responses and understanding regional difference of human activities under diverse geographic events. Finally, the study used urban rainstorm events as an example to examine the conceptualization and modeling method of geographic events. Social responses to urban rainstorms and regional differences were examined at inter-urban and intra-urban scales. The case study proved the concept and verified the feasibility and practicability of the proposed framework.