China's reform and opening up period saw a revival of research into population geography. Chinese researchers have discussed the issues of population capacity and realized that the total population of China will reach its maximum capacity and result in many social problems. The key to solving these problems is controlling total population capacity, developing production and changing lifestyles. Faced with resource shortages and environmental pollution, Chinese researchers have proposed strategies for creating a fourth industry, feeding environment, promoting labor employment, reducing environment pollution, and promoting gracious social behavior, cultural consciousness and new community organization at different scales. In response to rapid industrial shifts and various population structures, the research field proposed the theory of balanced population growth, and when faced with land use and development issues they developed a regional development model through industry transfer, population migration and payment transfer. Other themes covered in this review include unbalanced regional development, functional zoning indicators, a partitioned model of population development, population analysis, quantitative index and modeling. Future work on population geography in China requires (1) a distributed geographic information system around census and population thematic data to promote the exchange of population data and measurement models; (2) strengthening surveys of different micro-scale communities and control of the active behavior of community systems under rapid population change to improve our understanding and interpretation of quantitative population geography; and (3) international population intelligence exchange to better understand the population evolution trends of different countries, and regulate and control the allocation of labor and talent. Last, population geography researchers in China should adopt interdisciplinary methods to maximize their contribution to national development and scientific research.

1978年以来是中国人口地理学复兴和发展时期。中国人口地理学工作者消化吸收西方经典人口学理论,讨论中国人口容量问题,认识到中国人口总量即将达到增长极限,强调控制人口总量、努力发展生产和转变生存方式是解决人口问题的关键。针对资源短缺和环境污染问题,提出了创建第四产业,实施环境抚育,推动劳动力就业,降低环境污染的策略。针对民生问题,提出深入开展微观社会调查,主动再造跨尺度的社区制度,推进对人口行为的尺度综合和文化自觉。针对中国人口快速转变和人口结构问题,提出了人口均衡发展理论。针对国土空间开发格局问题,提出了区域发展均衡模型,强调通过产业转移、人口流动、转移支付等手段,形成相对均衡的区域发展格局。针对区域人口发展不平衡问题,提出了人口发展功能分区指标和分区模型,初步实现了视野综合化、指标定量化、分析模型化,将人口地理学研究推向新高度。未来中国人口地理学研究,一要围绕人口普查和人口业务数据库,建设分布式人口地理信息系统,推动人口专题数据和人口计量模型共享,巩固和发展人口地理学定量化研究之特色;二要加强不同尺度的社区微观调查,主动调控人口快速转变情景下的社区行为,提高对人口地理学定量研究结果的理解和解释;三要加强国际人口情报交流,把握各国人口演化趋势,从经济全球化的分工合作体系的视角,合理配置中国劳动力资源和人才资源。中国人口地理学应坚持走跨学科的发展道路,努力在世界人口之巅辛勤耕耘,为国家发展、学科建设做出应有的贡献。

China has witnessed unprecedented urbanization over the past decades. The rapid expansion of urban population has been dominated by the floating population from rural areas, of which the spatiotemporal patterns, driving forces, and multidimensional effects have been scrutinized and evaluated by voluminous empirical studies. However, the urban and economic development mode has been reshaped by the globalization and marketization processes and the socioeconomic space has been restructured as a consequence. How has the spatial pattern of floating population evolved against these backdrops? How has the evolution been driven by the interaction of state and market forces? What have been the contribution of population mobility to the urbanization of origin and destination regions and the evolution of China's urban system? The latest national censuses conducted in 2000 and 2010 offer the opportunity to systematically answer these questions. Analysis based on the county-level data comes to conclusions as follows. (1) The spatial pattern of floating population remained stable over the first decade of the 21st century. Three coastal mega-city regions, namely the Yangtze River Delta, the Pearl River Delta, and the Beijing-Tianjin-Hebei Region, were major concentration areas. As the emergence and rapid development of other coastal mega-city regions, the coastal concentration area of floating population tended to geographically united as a whole, whereas the spatial distribution within each region variegated significantly. (2) Floating population gradually moved into provincial capitals and other big cities in interior regions and its distribution center of gravity moved northward around 110 km during the study period. (3) Compared with extensively investigated inter-provincial migrants, intra-provincial migrants had higher intention and ability to permanently live in cities they worked in and thus might become the main force of China's urbanization in the coming decades. (4) The spatial pattern of floating population was shaped jointly by the state and market forces in transitional China. While the impacts of state forces have been surpassed by market forces in the country as a whole, they are still important in shaping the development space of central and western China. (5) The massive mobility of population contributed a large proportion to the increase of urbanization levels of both origin and destination regions and reshaped China's urban system in terms of its hierarchical organization and spatial structure.

基于2000和2010年全国人口普查分县数据,对中国流动人口空间格局的演变特征、形成机制及其城镇化效应进行了系统分析。研究发现,流动人口分布的空间格局具有较强的稳定性,长三角、珠三角和京津冀等沿海城市群仍然是其主要集中地,且沿海集中区有连绵化的趋势,但在城市群内部的空间分布模式差异显著。流动人口向内陆地区的省会等特大城市集中趋势明显,其分布重心出现了明显的北移。省内县际的流动人口规模已接近于省际流动,且有更高的意愿和更强的能力永久居留城镇,省内县际的永久性迁移将成为未来中国人口城镇化的主导模式。中国流动人口迁入地的选择受到政府和市场双重力量的影响,后者的影响力更强。远距离流入东部地区的人口在务工之外,对享受城市生活也开始有所考虑;而中西部地区政府力量在引导人口流动中仍起到重要作用。大规模的人口流动对流出地和流入地的城镇化水平提高均有显著贡献,同时在很大程度上重构了中国城镇体系的等级规模结构和空间布局模式。

This article reviews international literature on the changing trends of population migration and mobility and their mechanisms from the following perspectives: the changing trends of different forms of population mobility，the international comparison of the overall intensity of China’s internal mi- gration，the micro life course of population migration and mobility，and the mechanism and recent evolution of circular migration．The authors derive the following views on the future trends of China’s population migration and mobility from the above review and its implications: First，the recent decreasing trends of regional and rural-urban migration in China indicate changes in the forms of China’s population mobility rather than a real decline of its overall volume and intensity，which will still be on the rise; Second，great attention still needs to be paid to the portable issues of various public services provided to the floating population; and third，the management of and services to the floating population need to be improved in accordance with the changes in the forms of population mobility，especially the rise of urban to urban and intra-urban migration and mobility．

文章从人口迁移流动的不同形式及其演变趋势、中国国内人口迁移整体强度的国际对比、人口迁移流动的微观生命过程、以及人口循环流动的发生发展机制和近期演变等4个方面回顾了国际上对人口迁移流动演变趋势及其机制的相关研究,并根据从中获得的借鉴和启示对中国人口迁移流动的未来走势做出判断,认为目前我国人口在区域和乡城间迁移流动的减缓更多预示的是人口迁移流动形式的改变,而不是其整体规模和强度的下降,后者还有着相当大的上升空间;今后仍不可忽视针对迁移流动人口的各种公共服务的转移、接续问题,并要根据人口迁移流动形式的变化,尤其是人口在城市间和城市内部迁移流动上升的新形势,与时俱进地改进流动人口的管理和服务工作。

China is the most populous country of the world.Besides her great numberof population she has also the most densely inhabited regions which are notcomparable with any other country of the world.

年来中外学者,研究中国人口问题者,日见其多,中国人口是否过剩,国境以内,是否尚有大量移民之可能,此实当今亟须解答之间题,各方对此之意见,甚为纷歧;或则谓中国人口,实已过剩,此可由社会生计艰难,失业问题严重,以及海外侨民之多可以证之;或则谓中国人口,实未过剩,以全国面积除全国人口,计算其密度,较之欧西诸国,尚不及远甚,国境西北部,地旷而人稀,将来实大有移民之可能.

In the early 20th century, China was faced with domestic crisis and foreign invasion, and the man-land contradictions were unprecedented fierce. Geographers pondered and explored the issues of national fortune such as China's population status, northwest exploitation and internal migration, thus China's population geography emerged as the times required. "The distribution of population in China" published by Hu Huanyong in 1935 is a symbol of maturity of China's population geography. The Hu Huanyong Line (also known as Hu Line) proposed in this paper, which he originally called the Aihui-Tengchong Line, is a significant geographical demarcation of China's population. The existence and stability of the Hu Line have been repeatedly verified by census data, and its scientific principles have also been revealed and explained by the academic circles from aspects of nature, economy, social culture, etc. This paper points out that grain and employment are the two hidden logics behind the Hu Line. The Hu Line is becoming a crucial national geographic demarcation, which has an increasingly essential impact on the cognition and analysis of China's national conditions. Recent research on the Hu Line has been widely extended in various fields and meanings, and there arose some amendments and adaptations of the line in practice. Under the influence of "Premier Li Keqiang's three questions", whether the Hu Line can be broken through has become an academic hot spot. This paper holds that it is more important to create more opportunities of the northwest region than to increase the share of population so as to balance regional development.

20世纪早期,中国面临内忧外患、人地关系矛盾空前剧烈,地理学家对于中国人口国情、西北开发及国内移民等关乎国运问题的思考与探索,孕育了中国的人口地理学。1935年胡焕庸发表的“中国人口之分布”是中国人口地理学走向成熟的标识,文中提出的“瑷珲—腾冲线”即“胡焕庸线”,是中国人口地理的重要分界线。胡焕庸线的存在性与稳定性被人口普查等现实数据反复验证,其科学原理也被学术界从自然、经济、社会文化等方面加以揭示和阐释。本文指出食物与就业是胡焕庸线潜在的两大逻辑。胡焕庸线正在成为一条重要的国家地理分界,对认知与分析中国国情产生越来越重要的影响。近年来胡焕庸线的研究有了广泛引申,并衍生出多个领域、多种意义下的胡焕庸线,在应用层面上还出现了对该线的修正与变通。在“总理三问”的影响下,胡焕庸线能否突破成为一个学术热点,本文认为重要的不是增加西北人口份额,而是让西北地区获得更多发展机会,促进区域均衡发展。

The Hu Line for population distribution in China has been regarded as one of the greatest geographical discoveries in China because it reveals the significant spatial characteristics of China's human-land relationship. Thus, the stability and significance for spatial development of Hu Line have become a major concern after the dramatic economic and social changes since China's reform and opening-up in 1978. With the support of GIS, this paper conducts a statistical analysis and systematic investigation on the stability and spatial patterns of population growth on both sides of Hu Line by constructing the spatial database of China's census data from 1982 to 2010 and initiating a new method for identifying the spatial patterns of population growth. The findings are as follows: (1) The Hu Line has been rather stable, while a new tendency of population change has emerged. On the whole, the ratio of population on both sides of Hu Line has roughly been kept at 94:6 (the southeastern side: the northwestern side) in the last 30 years. However, the proportion of population on the southeastern side of Hu Line has been slightly decreasing, while that on the northwestern side of Hu Line has been slightly increasing, which is benefited from its higher rate of natural population growth. (2) The spatial patterns of population growth on both sides of Hu Line were quite different. The agglomeration degree of population distribution on the southeastern side of Hu Line increased greater. The areas with negative population growth rate have rapidly expanded, mainly located south of the Qinling Mountains - Huaihe River line and the northeastern China, while the areas with the fast population growth rate concentrated in the areas such as the Yangtze River Delta, the Pearl River Delta and Beijing-Tianjin metropolitan region. Thus, the spatial pattern of population growth on the southeastern side of Hu Line presented an aggregating and diffusion mode of Matthew effect. (3) The spatial pattern of population growth on the northwestern side of Hu Line could be referred as the relative balance type. In this region, the positive rate of population growth and the lower agglomeration degree of population have been identified. There were lots of ethnic groups located on the northwestern side of Hu Line, and they generally lived dispersedly but with a higher rate of natural population growth due to preferential population policy. However, there were also some areas with negative rate of population growth on the northwestern side of Hu Line and they were mainly distributed close to the Hu Line and new Eurasia Land Bridge. (4) In the future, the spatial patterns of population growth on both sides of Hu Line will continue to change. On the southeastern side of Hu Line, the capacity of population agglomeration for those small and medium-sized cities and towns should be enhanced. As for the northwestern side of Hu Line, the emphasis should be placed on promoting its urbanization and enhancing the capacity of population agglomeration for major cities.

“胡焕庸线”是反映中国人地关系的重要地理发现之一。在当今中国经济社会背景下,“胡焕庸线”所表达地理意义及其对城镇化发展的指导作用受到广泛关注。在GIS的支持下,构建了改革开放以来4次人口普查的县级空间数据库,提出人口时空扩张的识别方法,对“胡焕庸线”两侧的人口数量、集疏格局进行统计、分析,主要得出以下结论：① “胡焕庸线”两侧人口数量94:6的大数一直相对稳定,但东南半壁人口持续微减、西北半壁人口持续微增。得益于较高的自然增长率,西北半壁具有较高的人口增长速度。② “胡焕庸线”两侧呈现出迥然不同的人口集疏模式。东南半壁人口集中化程度提升较快,负增长区在“秦岭—淮河”以南、东北等地区大面积扩张、人口正增长优势逐步极化到长三角、珠三角、京津等少数地区,呈现“马太效应”式的集疏模式。主要是由于东南半壁内部区域经济差异及快速城镇化带来的剧烈人口流动。③ 西北半壁则呈现“相对均势”的人口集疏模式,多数地区的人口普遍表现为正增长,但是空间分布广袤、增长不集中,人口集中化程度提升缓慢。主要是由于少数民族“多分散、少聚居”造成了自然增长优势的不集中。然而均势是相对而不是绝对的,同样存在一定的负增长区,主要分布在“胡焕庸线”和“新欧亚大陆桥”两条带上。④ 未来时期,“胡焕庸线”两侧的人口分布及集疏格局将进一步演化,东南半壁应关注内陆腹地及中小城镇对人口的吸纳作用,西北半壁应关注将分散的人口增长优势向少数城镇进行集聚,以期为人口地理学研究以及城镇化发展提供参考。

In November, 2014, Premier Li Keqiang raised a problem about Hu Huanyong population line (hereinafter referred to as "Hu line"), when visiting the exhibition of sciences of human settlements in National Museum of China, which was called "Premier's Question" by the press. Hence, Hu line has become a highlight currently, and aroused great controversy and different views. Aiming at such dilemma of cognition, this paper gives a general review of the origins of Hu line, which was put forward by the famous population geographer Hu Huanyong in 1935, under the background of a debate on the surplus of domestic population. Based on population census data and GIS platform, the paper analyzes the change of population scale, proportion and density in both southeast and northwest sides of Hu line. The results indicate that the population urbanization and migration do not change the pattern of population distribution determined by Hu line. On such basis, the pattern that the population density of southeast part is large, while that of northwest part is relatively small will not radically change over a longer period, and the pattern that urban agglomeration is mainly located in southeast part as well. The long-term existence of Hu line depends on integrated physical geographical conditions, like climate. At the meantime, this paper argues that the core issue of the Premier's concern is solvable, by positive policy guidance and reasonable spatial organization. It is definitely promising for western China to realize a higher level of modernization and a better quality of urbanization, and central region as well.

2014年11月底,李克强总理在国家博物馆参观人居科学研究展时,向社会和科学界提出了关于"胡焕庸线"的问题,很多媒体称之为"总理之问","胡焕庸线"也因此成为时下受到高度关注的一个热词,就此开展了热烈讨论并提出了截然不同的见解.针对这样的认识困境,本文首先梳理了胡焕庸线的由来,是由著名人口地理学家胡焕庸先生于1935年提出,提出的背景是当时对国内人口是否过剩的大讨论.基于"一普","五普"和"六普"等人口数据和ArcGIS平台,分析了胡焕庸线东南半壁和西北半壁的人口规模,比重和密度变化,数据显示人口城镇化和人口迁移并没有改变胡焕庸线确定的人口分布格局.据此提出胡焕庸线揭示的人口东密西疏格局在较长时期不会发生根本性变化,城市群主要位于胡焕庸线东南半壁的格局在较长时期也不会发生变化,胡焕庸线不可破的原因是由气候等综合自然地理条件决定的.同时,本文认为总理关心的核心问题是"有解"的,通过积极的政策引导和合理的空间组织,西部地区完全可以实现更高水平的现代化和更好质量的城镇化,中部亦然.

Hu Line uncovers one of China's most important characteristics of population paper distribution: East is dense, while west is sparse. Different from most previous research, this paper examined the differentiation and changes of population distribution on both sides of Hu Line from a perspective of spatial stratified heterogeneity instead. Geodetector was employed based on the spatial database of China's census data of 1953, 1982, 1990, 2000 and 2010 to reconfirm spatial position of Hu Line and analyzed changes of spatial stratified heterogeneity of population between southeast and northwest sides of Hu Line in different periods. Changes of population distribution since the founding of New China were found and the reasons for these changes were discussed. Major findings include: (1) From the spatial stratified heterogeneity perspective, Hu Line could be improved and optimized, at least, in some periods. Although the ratio of total population on both sides of Hu Line has roughly been kept at 94:6 since 1953, spatial stratified heterogeneity of population between the two sides (the southeastern side: the northwestern side) increased when Hu Line moves to south slightly in 1953, 2000 and 2010, which means population distribution was more homogeneous within either southeastern or northwestern region and heterogeneity was more remarkable between the two regions. (2) Heterogeneity decreased gradually since the reform and opening up. We found characteristics of population distribution converged on the two sides, especially since the 1990s when convergence between the two sides became apparent. This finding is significantly different from the conclusion of "remain unchanged" from most literatures. The reasons why heterogeneity reduced were: pattern of population distribution on the southeastern side changed from relatively even distribution among cities before 1990 to agglomeration in a few huge cities after 2000, while the degree of spatial agglomeration of population decreased slightly after the reform on the northwestern side. These changes have been confirmed by the analysis from cumulative distribution function and Gini coefficient. (3) On the whole, the effect of economic factors on population distribution has become more and more important, while the effect of natural environment and institution reduced. Combined effect from economic development, natural environment and institution resulted in two opposite directions of changes of population spatial distribution on the two sides. It should be emphasized that although general effect of natural environment has decreased, some natural factors, such as Three Gradient Terrains, still have significantly influence on population distribution in China.

胡焕庸线作为人地关系的重要地理大发现之一,揭示了中国人口分布东密西疏的重要特征,是人文与经济地理学对社会的重要贡献之一。本文采用地理探测器等定量方法,以人口普查数据为基础,对胡焕庸线两侧人口分布的分异性特征进行了深入讨论,并尝试解释中国人口分布特征变化的原因及其机制。结果表明：① 胡焕庸线作为中国最重要的人口分界线仍基本保持稳定,但从空间统计学分异特征来看该分界线仍可进一步优化调整;② 胡焕庸线两侧内部人口集聚模式发生着明显变化,东南半壁人口分布由改革开放之前和初期的相对均衡状态,转变为以长三角、珠三角等少数区域为中心的集聚模式;而西北半壁人口分布的集聚程度则趋于下降;③ 从人口空间分布的影响因素看,尽管总体上,经济发展类因素对于人口空间分布影响不断增强,但三大阶梯等自然地理本底条件依然对中国人口分布有着重要影响。

The Tibetan Plateau is regarded as a typically sparsely populated area both from Chinese and global perspectives. There exists a large difference in population distribution of the Tibetan Plateau. Based on the town-level census data in 2010, we compiled a spatial population database to calculate the population density of the Tibetan Plateau. We found that the population distribution on this plateau was characterized in four dimensions, namely longitude, latitude, polarization and altitude. In addition, similar to the "Hu Line" for Chinese population distribution, we introduce the "Qilian-Gyirong Line" (short for Qi-Ji Line), a spatial division line of population geography in the Tibetan Plateau. Our main results are summarized as follows. (1) There are significant regional differences in the spatial population distribution in the Tibetan Plateau. The population density in the southeast was higher than that in the northwest. Compared to longitude-oriented, latitude-oriented and altitude-oriented regional differences, the polarization-oriented regional difference of population distribution was more prominent. This finding indicates that fewer people live in areas close to the cold-arid core of the Tibetan Plateau. (2) The spatial population distribution is closely related to the natural and environmental factors, including altitude, soil, water resources, climate and vegetation. The interaction between the natural factors has an impact on enhancing the regional difference of population. (3) The "Qiji Line" reveals the spatial differences of population in the Tibetan Plateau. The areas on either side of the line are approximately similar, whereas the population shares in the southeast and northwest halves are 93% and 7%, respectively. (4) In general, the population differences on both sides of the "Qiji Line" were stable over time. During 1982-2010 the population share in the southeast half decreased counterbalanced by an increased share in the northeast half. In the future, the majority of the people are expected to live on the southeast side. This is likely to imply two major policy initiatives. More attention is required on the urbanization development and transportation network construction in the southeast half and the increasing eco-environmental pressures from the growing population in the northwest half.

青藏高原是中国乃至全球典型的人口稀疏区之一,但内部人口地域分异明显。通过构建青藏高原乡镇街道尺度的人口空间数据集,系统核算青藏高原人口数量及其空间密度,从经度、纬度、极向和垂直4个维度解析青藏高原人口地域分异规律,并基于“胡焕庸线”思想,提出青藏高原的“祁吉线”人口地理划分方案。结论包括：① 青藏高原人口空间分布不均衡,具有“东南密、西北疏”的总体空间分布特征,距离“寒旱核心区”近疏远密的极向地域分异明显;② 青藏高原人口地域分异与海拔、土壤、水资源、气候、植被等自然环境本底具有高度耦合关系,自然因素间交互作用加强了人口地域分异;③ 青藏高原人口地域分异可以通过连接祁连县与吉隆县的“祁吉线”体现,两侧地域面积大致相同,但是东南半壁与西北半壁人口比例达到93∶7的悬殊;④ “祁吉线”长期稳定,但是东南半壁人口持续微降,西北半壁人口持续微增,未来时期,东南半壁依然是青藏高原城镇化及人类活动的主要区域,而西北半壁应当重视人口增长与生态环境压力的矛盾。

The utilization and expansion of urban construction lands produce a large amount of carbon emissions. Revealing the differences of carbon emissions of urban construction lands on the east and west of the Hu Huanyong Line and finding the driving factors can provide important references for the coordinated development of East and West China, carbon emission reduction, and new urbanization. However, there is a lack of comparative research on the changes of urban construction land and carbon emissions in these two regions. With the help of night light remote sensing data and GIS technology, a new method of extracting urban construction land was proposed, and the urban construction lands east and west of the Hu Huanyong Line were extracted and analyzed. The carbon emissions from the urban construction lands were estimated and analyzed through applying the carbon emission estimation methods of relevant literature. Based on these results, the correlations between urban construction lands and carbon emissions were analyzed. Combining with socioeconomic data, the results were discussed in depth. This work indicates that: (1) The results of the boundary-threshold method were better than that of the empirical threshold method and the neighborhood analysis method. (2) The Hu Huanyong Line has the possibility to be broken. From 2000 to 2013, the ratio of the areas of urban construction lands between the east and the west lowered from 95:5 to 92:8. (3) The rapid development of the western regions is at the cost of high carbon emissions. The ratio of annual carbon emissions between the east and the west lowered from 93:7 to 90:10. (4) According to the average level, when the urban construction land in the east and west increased by 1 km2, annual carbon emissions of urban construction land increased by 17.94 thousand tons and 25.75 thousand tons, respectively. While continuing to pay attention to the eastern regions with a large amount of carbon emissions, China should also pay attention to the exacerbating problem of high carbon emissions in the western regions. Methods such as promoting intensive use of urban construction land, optimizing industrial structure, and advocating a green and low-carbon lifestyle can be taken to help the western regions to embark on a new road of intensive and low-carbon urbanization.

城镇建设用地在利用和扩张过程中承载和拉动着大量的碳排放。揭示胡焕庸线东西两侧城镇建设用地的碳排放差异,并探讨其驱动因素,能为东西部的协调发展、碳减排工作和新型城镇化提供重要参考。本文借助夜间灯光遥感数据和GIS技术,提出了边界阈值法,对胡焕庸线东西两侧的城镇建设用地进行了提取和分析,并综合相关文献中的碳排放估算方法对其所承载的碳排放进行估算和分析,在此基础上,对其关联性进行了剖析,并结合相关社会经济数据对研究结果进行深入讨论。研究表明：①边界阈值法提取结果的检验结果较好,优于经验阈值法和邻域分析法。②胡焕庸线存在被打破的可能性,2000—2013年东、西两侧城镇建设用地的面积比从95：5变为92：8,差异缩小。③西部地区的快速发展是以高碳排放为代价的,2000—2013年东、西两侧年碳排放量比值从93：7变为90：10,差异缩小。④东、西两侧的城镇建设用地每增加1 km²时,年均碳排放量分别增长1.79万t和2.58万t。因此,国家在继续重视碳排放量较大的东部地区的同时,也应重视西部地区加剧的高碳排放问题。可通过引导城镇建设用地的集约式扩张、优化产业结构和提倡绿色低碳的生活方式等手段促使西部地区走上集约低碳的新型城镇化道路。

Hu Huanyong, a famous geographer, discovered a divide of population geography in China in 1935 (hereinafter referred to as the Hu Line), which was an important achievement in the development of the discipline of geography in China, and was widely accredited and cited. In November, 2014, Premier Li Keqiang raised a question about the Hu Line, when he visited the exhibition of sciences of human settlements in the National Museum of China. This question is whether the Hu Line can be broken or not again caused a stir. Hereby we invited some geographers to have academic discussion on this question, aiming to demonstrate their understanding and reflection on the Hu Line from different perspectives. Thus, the scientific value and practical significance of the Hu Line are deepened, and furthermore, the Hu Line can provide reference for the implementation and regional planning of the new-type urbanization in China.

著名地理学家胡焕庸先生于1935年提出中国人口地理的重要分界线（简称“胡焕庸线”）,被广泛认可和引用,是中国地理学发展的重要成果。2014年底,李克强总理参观人居科学研究展时,高度关注胡焕庸线,并提出了胡焕庸线能否突破的问题。胡焕庸线因而再度引起争论和热议。据此,组织了一些地理学者围绕该问题进行学术讨论,力图从不同层面展现学者们对胡焕庸线的理解与反思,从而深化胡焕庸线的科学价值和现实意义,进而指导中国新型城镇化战略的实施和区域实践。

The Hu Huanyong Line, which is also called the Aihui-Tengchong Line, is drawn by Hu Huanyong and marks a striking difference in the distribution of China's population. It has been accepted and used for the last 81 years, and has had a considerable influence on Chinese population distribution research at home and abroad. With rapid new urbanization, research on the Hu Huanyong Line has increased sharply. In the context of new urbanization, an urgent question for us is how to understand the Hu Huanyong Line accurately. As a divide between the distribution patterns of the population in China, the Hu Huanyong Line has not changed substantially in the past 81 years. It represents a divide not only for the ecological environment, but also for climate. There are mainly prohibited development areas and restricted development areas in the Major Function Oriented Zones Planning west of the Hu Huanyong Line. It is not only the region east of the Hu Huanyong Line, but also includes some parts of the central and western regions of China. The formation of the line was the result of long-term interactions between the natural environment, economic development and social and historical conditions. Therefore, it would not be changed by what we think and do to break through. New urbanization emphasizes that the rural population migrates to the towns and cities nearby, rather than a large-scale transfer of population. Due to a local transfer of 100 million people in the central and western regions, new urbanization will accelerate the process of the population gathering in these regions. New urbanization has a significant impact on the population structure of different sizes of cities and towns, but little effect on the national spatial pattern. It is healthy urbanization in harmony with nature, therefore, rational thinking is required during the process of new urbanization, in order to optimize the spatial distribution pattern of urbanization. Pushed by the two-child policy issued recently, the population in the eastern and central China is predicted to increase with the western region increasing slowly due to the unbalanced population birth policy. With the implementation of the Belt and Road Initiative, urbanization in the western region will accelerate, opening up and expanding border cities, thus posing new challenges to the population distributed either side of the Hu Huanyong Line.

“胡焕庸线”提出80年来,在国际上产生深远影响。随着中国新型城镇化进程的全面推进,对胡焕庸线的研究急剧升温。在新的历史背景下,如何客观看待胡焕庸线成为亟待解决的一个问题。研究认为：胡焕庸线不仅是中国人口分布的分界线,也是重要的自然生态界线,这条界线的形成不以人的意志为转移,不宜人为去“打破”。同时,在新型城镇化背景下,应该树立理性思维,稳妥有序地推进城镇化进程,不断优化城镇化的空间分布格局。在全面放开二孩的新政策推动下,由于中国区域人口政策的差异性,东部和中部地区的人口有望实现较为明显的增长,西部地区增长相对缓慢,由此可能对胡焕庸线两侧的人口空间格局产生一定的影响。

The definition of city is connected to administrative division system in China. It is important to understand the spatial difference between city administrative area and city physical area. According to the population census data in 2010, we distinguished city definitions in multiple administrative levels, including municipality cities, prefectural cities, cities with districts, cities without districts, cities with sub-districts and cities without sub-districts. In addition, we compared the spatial areas between city administrative cities and physical cities area and put forward some integration strategies. The main results are listed as follows. (1) Among various administrative cities, municipality cities and prefectural cities were larger. The following ones were cities with districts and cities without districts. The areas of cities with sub-districts and cities without sub-districts were relatively small. City physical area reflected the real landscape of a city, which was smaller than all kinds of city administrative areas. It only covered 0.32% of the whole area in the mainland of China but had 30.18% of Chinese population in 2010. (2) To classify city scale hierarchies, the population in city physical area was a better measure than the population in city administrative area. According to the population in the physical area, Shanghai is the largest city in China in 2010. (3) China's city physical area definition was also affected by city administrative definition. We suggested China's city administrative division adjustment should concerns more on county-to-city conversion and new prefectural-city establishment. It is better to regard the population city physical area as a reference index for administrative division adjustment. For the definition of the city physical area, independent municipal district, county seat and large towns were suggested as the independent city physical area. Besides, we recommended to open the statistical data related to city physical area. We do hope our research can be beneficial for policy implications for China's administrative adjustment and city physical area studies.

中国的城市界定与行政区划紧密关联。根据2010年人口普查数据,系统分析不同尺度城市行政地域与城市实体地域的界定及其空间差异。主要结论：① 按照直辖市或地级市、设区的市和不设区的市、设街道的市和不设街道的市的层级,城市行政地域范围依次收缩,但是都大于城市实体地域范围。按照实体地域界定,2010年中国城市人口仅占30.18%。② 城市实体地域更能客观地反映城市位序规模的分布状态,而按照城市行政地域会导致规模或排序偏差。③ 未来在行政区划调整时,着重考虑撤县设市、增设地级市、确立乡级行政区划调整标准等,在建立城市实体地域时,可从独立市辖区、县城、特大镇等方面优化,并加强统计信息公开。

Spatial stratified heterogeneity is the spatial expression of natural and socio-economic process, which is an important approach for human to recognize nature since Aristotle. Geodetector is a new statistical method to detect spatial stratified heterogeneity and reveal the driving factors behind it. This method with no linear hypothesis has elegant form and definite physical meaning. Here is the basic idea behind Geodetector: assuming that the study area is divided into several subareas. The study area is characterized by spatial stratified heterogeneity if the sum of the variance of subareas is less than the regional total variance; and if the spatial distribution of the two variables tends to be consistent, there is statistical correlation between them. Q-statistic in Geodetector has already been applied in many fields of natural and social sciences which can be used to measure spatial stratified heterogeneity, detect explanatory factors and analyze the interactive relationship between variables. In this paper, the authors will illustrate the principle of Geodetector and summarize the characteristics and applications in order to facilitate the using of Geodetector and help readers to recognize, mine and utilize spatial stratified heterogeneity.

空间分异是自然和社会经济过程的空间表现,也是自亚里士多德以来人类认识自然的重要途径。地理探测器是探测空间分异性,以及揭示其背后驱动因子的一种新的统计学方法,此方法无线性假设,具有优雅的形式和明确的物理含义。基本思想是：假设研究区分为若干子区域,如果子区域的方差之和小于区域总方差,则存在空间分异性;如果两变量的空间分布趋于一致,则两者存在统计关联性。地理探测器q统计量,可用以度量空间分异性、探测解释因子、分析变量之间交互关系,已经在自然和社会科学多领域应用。本文阐述地理探测器的原理,并对其特点及应用进行了归纳总结,以利于读者方便灵活地使用地理探测器来认识、挖掘和利用空间分异性。

Boundary of eco geographical regions is based on a set of index that indicates the regional features. It is located on special location by spatial differences in environmental features. Impersonally recognizing and delineating the boundary is an important way to open out spatial order of the environment. This boundary is a line or belt as border for two joined regions with different features. It shows relative coherence in environmental features within a region and otherness to the other region. The boundary is a belt with wideness that can be changed as course of time. Higher-class regions have wider boundary and lower class regions have clearer boundary. In delineation of eco geographical regions, several factors that can hardly be controlled by human are selected as main indexes. Days and cumulated temperature of daily temperature ≥10℃, average temperatures of the coldest and hottest months are used as indexes of temperature state. Dryness is the most common factor as token of dry humid degree of a region. Annual precipitation is more reliable but calculation of latency evaporation should be improved. Division of higher class of eco geographical regions focuses on biological and climatic differences, first of all on horizontal zonality. Because of limitation of number of climatic stations, the boundary is always modified with vegetation. Vertical zonation links latency vegetation with climate, which is divided according to precipitation, potential evaporation and bio temperature relationship. How to deal with relation between classes and indexes of eco geographical regions is another important point. Some studies tried to combine indexes of natural factors with social economic factors. Some considered the index system should cover environmental, resources, economic, social and population factors. Some proposed taking temperature, water moisture factors for the higher classes and introducing resources and social-economic factors for the lower classes. However, the former has not given detailed index and the latter took different indexes for different regions, which should have more work to realize the combination.

 The “Hu Line”and its demographic implications have attracted world-wide attention since the line was developed 80 years ago．Using GIS，this paper conducts a statistical analysis and systematic investigation on the stability and spatial patterns of China’s minority population growth on both sides of“Hu Line”by constructing the spatial database of China’s census data from 1953 to 2010 and initiating a new method for identifying the spatial patterns of population growth．Major findings are as follows: ( 1) Spatial distribution of the minority population in China is not balanced，showing a signifi- cant spatial clustering; ( 2) The minority population is widely distributed across China，spreading to East China and all over the country; ( 3) The distribution pattern of China’s minority population is characterized by extraordinary stability，with the share ratio of south-east half to north-west half standing roughly at 75: 25 from 1953 to 2010．We can thus say that the“Hu Line”is also a mutant line of China’s minority population．

 "胡焕庸线"作为中国人口的突变线,从1935年提出至今的80余年里,在国内外引起广泛的关注和深刻的思考。文章从民族人口的视角出发,收集和整理1953~2010年期间六次全国人口普查的县级资料,运用Arc GIS、Geo Data的空间分析技术,对"胡焕庸线"两侧的民族人口分布状况、变动趋势进行统计和分析。结果表明:中国少数民族人口空间分布不均衡,具有显著的空间集聚性,少数民族人口在传统分布区形成多个热点分布区域;中国少数民族人口分布广泛,民族人口向东部地区乃至全国范围迁移扩散的态势显著;中国少数民族人口分布格局具有非凡的稳定性。从1953~2010年东南半壁和西北半壁少数民族人口75∶25的比重一直相对稳定,可以说"胡焕庸线"也是中国少数民族人口的突变线。

Based on the data of usual residence from 2000 and 2010 censuses and 1995 and 2015 micro-censuses and using the method proposed by Abel G. J., this paper estimates the O-D migration flows among prefectural-level administrative units in China for the period 1995-2015. By using the indicators of migration flows and migration rates, and the methods of GIS spatial analysis and community detection in social network analysis, it further reveals the characteristics of spatio-temporal evolution of migration in China since 1995. The results can be summarized as follows. (1) The scale and intensity of migration in China have been increasing, while their differences among regions have been gradually decreasing. This suggests that migration has experienced a gradual transformation from a "low-activity era" including a limited number of regions to a "high-activity era" involving the majority of regions. (2) Six regional types of migration among prefectural-level administrative units, namely, large-scale active net in-migration, small-scale net in-migration, large-scale active net out-migration, small-scale active net out-migration, active balanced migration and inactive migration, are identified. The spatio-temporal evolution characteristics of the regional types of migration in China indicate that each active migration regional type has been undergoing a change of continuous diffusion, while the inactive migration regional type has seen a significant reduction over time. (3) The spatial patterns of migration are quite different between regions on both sides of "Hu Line", manifested in the fact that the scale and intensity of migration flows on the southeastern side of the line is higher than that on the northwestern side, which means that the "Hu Line" is quite stable and robust in the last 20 years. (4) Patterns of migration flows indicate that while intra-provincial migration has continuously strengthened, inter-provincial migration has exhibited more complicated spatial patterns, mainly reflected in different changing trends of attractiveness to migrants among the three coastal city clusters, and the increasing migration flows within southwest China. As a result of combined effects of inter- and intra-provincial migration flows, the structure of migration flows in China's eastern, central and western regions has been undergoing changes, resulting in the internal differentiation of urban agglomerations and the declining spatial scope under their influence in the coastal areas, Hubei as the single independent "city community" in central China, as well as the relative stability in northwest China and continuous change in southwest China.

本文利用人口普查数据,估算了1995—2015年中国地（市）间人口O-D迁移流和迁移率,结合GIS空间分析和社会网络分析方法,揭示了20年间中国人口迁移的时空变化特征。研究发现：① 中国人口迁移由相对不活跃、局部地区参与的“低活性时代”,逐步走向相对活跃、绝大多数地区参与的“高活性时代”。② 人口迁移地域类型的时空演化过程呈现出各活跃型地（市）不断扩散,而非活跃型地（市）大幅缩减的特点。③ 人口迁移网络以“胡焕庸线”为界,东、西两侧迁移流“东密西疏”且差异悬殊,这一空间格局具有很强的稳定性和顽健性。④ 在人口省内迁移持续增强,以及跨省迁移中沿海三大城市群吸引力的“此消彼长”和西南地区吸引力不断增强的背景下,东中西部地区的人口迁移流场结构表现为：沿海地区主要城市群内部分化和影响范围减弱,中部地区（除湖北省）未能演化出以省为单元的独立社区,西部地区则是西北相对稳定而西南持续变动。

Using data of the latest three decennial censuses, this paper systematically analyzes the overall spatial pattern, changing trends, and influence mechanisms of China's population distribution since 2000. The study reveals that the general population distribution pattern of "dense east and sparse west" in China has not changed, which is determined by the differences in natural geographic environments on the two sides of Hu Line. In the first decade of the century, population concentration was mainly found in the southeastern area, but it has been observed in all regions in the recent decade. Provincial capitals have become the winners of population competition and the advantages of population growth of provincial capitals have been further strengthened in the recent decade compared with 2000-2010. However, the administrative power-led effects of the increasing dominance of provincial capitals will gradually weaken with the development of their provinces. The regional differentiation of population changes is also apparent: coastal region gradually forms a dense belt of population and towns with solid population attraction based on the development of urban agglomerations; the northeast region almost turns to a complete population shrinking status; central provinces still compete fiercely for population based on their capitals; the population of Sichuan, Chongqing, and Guizhou has stopped the decline and returned to growth; and the northwest region faces the risk of population loss. In addition, this paper finds that the driving factors of regional population growth have gradually changed from economic factors to both economic and amenity factors, and the difference of amenities among regions may become an important factor for future changes in China's population geography.

基于第五、六、七次全国人口普查数据,本文分析了2000—2020年中国人口分布的空间格局、集散态势和影响因素。结果表明,中国人口分布依然保持东密西疏的基本格局,胡焕庸线两侧的自然地理环境差异性决定了这一格局的长期稳定性;人口空间集中化趋势在21世纪初的10年内主要发生在东南半壁,但在2010—2020年间成为各区域的共同特征。省会城市的人口集聚能力持续增强,2010—2020年的优势更加凸显,但这种行政力量主导的首位度提升效应将随着全省发展阶段的演进而逐渐弱化。人口变动的区域分化明显：沿海城市群的空间连绵化逐渐形成了强吸引力、高承载力的沿海人口增长带,东北地区几乎转向全面的人口收缩,中部各省依托省会展开的人口竞争依然激烈,川渝黔地区普遍实现了人口的止降回增,西北地区则面临人口收缩风险。此外,区域人口增长的驱动因素逐渐从经济要素主导转为经济要素和舒适性要素并重,各地区舒适性的差异可能将成为影响未来人口空间格局变化的重要因素。