Temporal And Spatial Pattern Evolution Of Urban Agglomeration In Hainan Island Based On Night Light Image Data

As an important symbol in the process of regional industrialization and urbanization development,town clusters are the spatial carrier leading the regional development.Hainan Province is located in the southernmost part of China.As one of the earliest special economic zones in China,it is located in the southeast coastal areas of China and has a relatively high degree of opening to the outside world.However,after more than 30 years of development,the overall development speed of Hainan Island is not only far behind the coastal areas of China,but also lower than the national average level.In 2018,the Hainan Island Free Trade Zone was established.In the new historical period,how to grasp the opportunity of urban development and build the city cluster of Hainan Island into a new growth pole in the southeast coastal areas of China has become one of the main problems facing the development of the city cluster of Hainan Island.Nighttime light data can directly reflect the intensity of human social and economic activities,and because of its advantages such as easy access,long time sequence and large space span,it is often used in the monitoring of urbanization process and the exploration of the evolution pattern and law of urban agglomeration.Based on the DMSP/OLS and NPP/VIIRS two night lights data as the foundation,to extract the range 2005-2019,hainan island city cluster proper space,using the analysis of dynamic change,urban hainan island city cluster night first degree analysis,natural eco-space space-time evolution pattern of space from the correlation analysis to explore the rule of hainan island city cluster urban sprawl.In addition,indicators such as physical geographical factors,population flow,economic factors and urbanization level are selected to explore whether there is a correlation between urban expansion of Hainan Island city cluster by using Granger causality test.The main research contents and relevant conclusions are as follows:(1)the hainan island city cluster growth pole of urban expansion mainly concentrated in the hainan island city cluster of city cluster at the center of the city,haikou city,danzhou,sanya three cities of the total contribution to high growth of noctilucent lamp of hainan island night-light growth from 2005 to 2019,70.29% of the total development faster,three cities in the economic activity leads the island economic development;Based on the analysis of the city cluster primacy degree of Hainan Island,the overall city size distribution of the 18 counties and cities in Hainan Island is relatively dispersed,and the first city effect is not significant,so the development of the first city should be enhanced.For the four sub-city clusters,the primacy degree is high and the primacy city effect is significant,and the difference between the first city and other cities is great within each sub-city cluster region.Based on the spatial and temporal pattern evolution of Hainan Island city cluster,it is found that the urban expansion speed of Hainan Island city cluster is significantly lower than the national average level,and the urbanization level is much lower than the eastern coastal areas of China.Through the analysis of urban spatial autocorrelation,it is found that there is obvious agglomeration phenomenon in the urban agglomeration of Hainan Island,and the main agglomeration hotspot is the central city of the urban agglomeration and the central city of the sub-urban agglomeration of Hainan Island,while the central mountainous area is the cold point area of spatial agglomeration.(2)The natural geographical factors of Hainan Island are the main factors restricting the urban expansion of city clusters.However,with the passage of time,both positive and negative natural factors gradually weaken the economic influence,and the expansion of city clusters of Hainan Island is gradually getting rid of the influence of natural geographical attributes.Based on the Granger causality test of population flow and urban built-up area,it is found that population flow is the cause of urban built-up area expansion of Hainan Island city group,but the expansion of built-up area is not the cause of population flow.In other words,population inflow can positively influence urban built-up area expansion to a certain extent.On the other hand,the expansion of urban built-up areas does not lead to population inflow.Based on economic factors and granger causality test to the geographical expansion of cities found that economy and urban expansion,obvious granger causality relationship between each other,which means the increase of the economy affects the urban sprawl,and urban sprawl positive influence on economy increase,and the first industry and city cluster urban expansion cause and effect is not obvious,especially the granger causality of hainan island city cluster of the third industry is more apparent,suggests that the third industry is the main factors influencing the hainan island city cluster urban sprawl;Through the Granger causality test of the main indicators of urbanization level and urban expansion,it is found that urbanization indicators and urban expansion are mutual causes,and there is a significant positive correlation between the two.