Make the map visual! She uses geographic information system to reflect the real world

The ancients used maps to depict spatial information, while modern people use geographic information systems (GIS) to reflect the real world.

GIS is a computer-based tool that can manage, analyze, and integrate spatial information. More than ten years after the birth of the world's first practical GIS, my country also began to develop GIS in 1977. Over the past half century, China's GIS has evolved from imitation to independent research and development, and has continuously integrated with advanced technologies and gradually applied to all aspects of national economy and people's livelihood. This is inseparable from the exploration of theories, methods, and applications by a large number of teaching and research personnel, as well as their efforts in talent training.

▲Pu Yingxia (second from left) defended her master's degree thesis in Cartography and GIS at Nanjing University in 2021

Pu Yingxia, an associate professor from the School of Geography and Ocean Sciences of Nanjing University, is just such a scientific and technological worker who has been working on the front line of GIS teaching and research in my country for a long time. Since the 1990s, Pu Yingxia has kept up with the forefront and has successively opened important courses such as map projection, map analysis and application, spatial econometric model and spatial data analysis. She has made a series of innovative and practical achievements in the integration of GIS and spatial data analysis theory and methods and its application in regional analysis, nurturing many outstanding students, and witnessing and participating in the 30 years of hard work and development of China's GIS.

Continuous improvement to promote the development of China's GIS

The wind starts from the tip of the green apple, and the waves form from the ripples. This sentence is a true portrayal of the development of China's GIS and a vivid description of Pu Yingxia's work life.

In 1990, Pu Yingxia was admitted to the Department of Geography of Shandong Normal University. During her undergraduate studies, she developed a strong interest in quantitative geography. In 1994, Pu Yingxia was admitted to the School of Geography and Ocean Sciences (formerly the Department of Geography) of Nanjing University, which is known as the cradle of Chinese geography, to pursue a master's degree in cartography and geographic information systems. She graduated three years later and stayed at the university to teach. At that time, domestic GIS research had just started, and there was a lack of talent in geographic information science at Nanjing University. Pu Yingxia faced both opportunities and challenges.

Map projection was the first course Pu Yingxia took. "I have studied cartography, but I have not done any special research on map projection, and the advanced mathematics knowledge used in it is also difficult." In order to tackle this difficult problem, she studied hard on her own, asked for advice humbly, accumulated a thick set of teaching plans and notes, and gradually became independent. In 1999, in order to be better qualified for scientific research, Pu Yingxia began to pursue a doctorate and conducted in-depth research on spatial data analysis. After graduating with a doctorate, she applied for and was approved for her first important project in 2006 - the National Natural Science Foundation Youth Project. Taking the economic and social data of Jiangsu Province as an example, she discovered spatial correlation patterns from the GIS database, thus officially starting her scientific research career. She started with regional data analysis and gradually deepened the complex population migration data analysis.

In 2008 and 2017, in order to improve her academic research, Pu Yingxia visited the China Data Research Center at the University of Michigan and the Department of Rural Economy, Society and Education at Pennsylvania State University for exchange visits. In recent years, she has combined international cutting-edge research with her own experience and opened a spatial data analysis course that involves a lot of advanced mathematics, probability theory, statistics knowledge and covers complex GIS technology. In this regard, Pu Yingxia said: "A discipline is always becoming more and more complex as it develops, and it constantly places higher demands on researchers. Only by keeping pace with the times and continuously learning and accumulating can we adapt to the development needs of the discipline and achieve better results."

Thanks to this, Pu Yingxia has published more than 90 academic papers at home and abroad so far; participated in the completion of the monograph "Discovery of Spatial Correlation Patterns in GIS"; participated in the writing of three textbooks, "Application of Geographic Information Technology", "Map Projection" and "Cartography". In 2021, she won the first prize of Jiangsu Science and Technology Award and the Science and Technology Progress Award of China Geographic Information Industry Association for "Key Technology and Decision Support of Geographic Information Cloud Service Platform" and "Research on Key Technology for Building a 'One Map' Governance System for Natural Resources and Planning at the District and County Level". Pu Yingxia has contributed her own strength to the development of GIS in China with practical actions.

Analyzing population migration with spatial data

Because of the spatial location attribute, spatial data are interconnected and have the characteristics determined by the first law of geography - everything is related to other things, but similar things are more closely related. Spatial autocorrelation research has a wide range of applications and can play an important role in social economy, human history, physical geography and other fields. Among them, population migration is one of the key topics that Pu Yingxia studies using spatial data analysis methods.

After the reform and opening up, "peacocks fly southeast" has become a new trend of population migration; since 2010, my country's economic growth has gradually slowed down, and part of the population has returned to the central and western regions. At the same time, as my country's population growth slows down or even shows negative growth, population migration is becoming an important way for regional population growth. In Pu Yingxia's view, population migration not only depends on the natural, economic, social and cultural attributes of the place of departure and the destination, but is also closely related to the various states of previous population migration and current surrounding population migration, and has a profound impact on future population migration. Exploring the influencing factors and spatiotemporal dynamic mechanisms of regional population migration is a practical need to ensure the relative balance of regional population redistribution in my country, the smooth flow of human resources, and the improvement of the market-oriented allocation mechanism of factors.

In view of the fact that most traditional modeling and analysis are based on cross-sectional data and gravity models, focusing on the "push and pull" effect of bilateral elements at the starting and ending points, while ignoring the organic connection of time and space dimensions and rarely considering uncertainty issues, Pu Yingxia introduced and deeply analyzed the Bayesian model averaging method to solve the problems of variable selection faced in the modeling process. "I learned more about Bayesian statistics during my visit and exchange at Pennsylvania State University. Bayesian statistics uses prior knowledge and sample information to obtain posterior probabilities through Bayesian rules to solve statistical problems such as parameter estimation, hypothesis testing, prediction and decision-making. The interesting thing about this method is that it puts the intensity of people's belief in the occurrence of things at the core, which has a great impact on me."

For example, when carrying out the National Natural Science Foundation project "Spatial OD (origin and destination) model optimization and uncertainty analysis", Pu Yingxia started from the complexity of the network system where the spatial OD flow is located, and combined with Bayesian statistics to establish a spatial OD model that represents uncertainty, focusing on the possible uncertainties in the expression of node attributes, node environment and model structure. The model was optimized by the Bayesian model averaging method, in order to make a more scientific explanation of the pattern evolution and internal mechanism of the spatial OD flow, and to make a probabilistic prediction of future development trends. Related research has demonstrated the feasibility of the construction and optimization of spatial OD models facing uncertainty in terms of technology and methods through modeling and predictive analysis of inter-provincial population migration flows in China.

In the research of the National Natural Science Foundation of China's general project "Optimization of Spatial Dynamic OD Panel Model and Analysis of Spatiotemporal Dynamic Mechanism", which was approved in 2023, Pu Yingxia focused on the uncertainty in the expression of the starting and ending point elements, surrounding environment and spatiotemporal structure of the network system where the OD flow is located. Through convex combination and Markov chain-Monte Carlo model synthesis, all possible models are weighted averaged with a posteriori probability as weight, and the spatial dynamic OD panel model is constructed and optimized to quantitatively explain the internal mechanisms such as the spatiotemporal path dependence and network spillover effect of the development of OD flow. Through the modeling and analysis of China's inter-provincial population migration flow since the reform and opening up, it shows the feasibility of the optimization of the spatial dynamic OD panel model in theory, technology and method under the background of uncertainty, which will deepen the research and application of GIS spatiotemporal data mining and provide decision support for the formulation of regional population migration policies and the improvement of market-oriented allocation of factors.

Provoking more thinking through academic research

"In addition to population migration, logistics and information flows are all flowing information, involving the interaction between two regions or even multiple regions. The more factors are considered, the more difficult the modeling analysis will be." Pu Yingxia led the students to analyze, estimate, and verify patiently and meticulously over and over again, constantly achieving the expected results and providing decision support. "At the same time, the time and space concepts involved in population migration also provide us with a broader background to explore population issues. By studying population migration, the most important thing is to show the network spillover effect in population migration and trigger more thinking among people."

This research intention and research method not only attracted domestic graduate students, but also Belarusian graduate students who saw Pu Yingxia's research articles online and came here. "In 2022, I also tried to jointly apply for an international cooperation project on transportation and tourism with a professor of economics at the University of Bologna, Italy. Although it was ultimately unsuccessful due to lack of cooperation experience, it laid the foundation for future cooperation." Nanjing University has an open-minded school spirit, and Pu Yingxia also has very few restrictions on students. "My project time is relatively ample. While promoting teamwork to advance scientific research projects, I hope to teach students the knowledge and skills that combine theoretical and practical tools, and give them space to let them freely explore the directions of their interests."

In 2020, Pu Yingxia officially stopped teaching the "Map Projection" course she had taught for 20 years. At a meeting in November 2023, she met a student from more than a decade ago. The student told her that thanks to the learning at that time, whenever colleagues encountered problems related to map projection in the unit in recent years, they would come to consult him, and their words were full of pride. The seeds sown in the classroom took root and sprouted in places she could not see as the students scattered into society. Pu Yingxia, who was originally quite regretful about the suspension of classes, was comforted by this. In the future, she hopes to keep up with the forefront, make more achievements in the field of GIS, and continue to benefit society.