TOWARD ESTABLISHING THE CONCEPT OF PHYSICAL URBAN AREA IN CHINA

This paper makes a detailed analysis of the vanous drawbacks of the continued use of adwhnistrative area in dividing urban and rural areas in spite of the serious discrepancies between urban admnistrative boundaries and the 'real' urban space in China. The autiors believe that to solve this problem, it is essential to establish the concept of physical urban area with both adaptability to Chinese situation and intemational comparability and use it as the basis of urban-rural division and statistics. It is proposed that physical urban area should be defined in terms of prescribed minimum population scale, dngee of nonaghculturalization and population density.Based on extensive substantive research and a classifiotion of the space figurations of Chinese cities and towns, a new scheme to classify physical urban areas is proposed.

Quantitative Analysis of Spatial Vitality of Urban Built-up Area: A Case Study of Shenzhen

As an important goal of urban design research,the evaluation of urban spatial vitality has been widely concerned.Taking Shenzhen as an example,the urban built-up area of Shenzhen was identifi ed using improved DENsi-Graph analysis,from the perspective of quantifi cation of urban spatial morphological features.The accessibility of urban streets,degree of construction and architectural form,and degree of functional mixing were quantitatively analyzed through space syntax,space matrix and mixeduse index(MXI),and the spatial vitality of urban built-up area was evaluated.Research results demonstrated that the improved Densi-Graph analysis could better identify the built-up area of Shenzhen,and the overall classifi cation accuracy was 0.810.The analysis results of spatial vitality showed that the urban spatial vitality in Shenzhen urban built-up area was well created.The street accessibility of Shenzhen generally hindered the creation of urban vitality;the spatial matrix value in the north of Shenzhen urban built-up area was lower;and the MXI of most areas within the study area was above the medium.

School and community physical activity characteristics and moderate-to-vigorous physical activity among Chinese school-aged children： A multilevel path model analysis

Purpose: The purpose of this study was to examine the association between school and community physical activity(PA) characteristics and levels of moderate-to-vigorous physical activity(MVPA) among Chinese school children.Methods: Data were obtained from the 2016 Physical Activity and Fitness in China—The Youth Study project. Participants were 80,928 school children(Grades 4–12; 39,747 boys, 41,181 girls; mean age = 13 years) and 935 physical education(PE) teachers who completed a study survey.Independent variables included both school-related factors(school-level PA support, availability of and access to PA facilities, and the duration of school PE classes) and community-related factors(the frequency of sports events, sports training opportunities, availability of sports clubs and organizations, and access to PA facilities). The dependent variable was the children's self-reported participation in MVPA. The data were analyzed,in 2017, via multilevel modeling.Results: PA support from school administrators was the only school-level factor significantly related to children's participation in MVPA.Children's perceptions of the frequency of community-sponsored sports events, availability of sports clubs and organizations, and convenient access to PA facilities were associated with a high level of MVPA participation. In regard to residency in urban and rural areas, children attending urban schools who perceived high availability of PA facilities were associated with a low level of participation in MVPA.Conclusion: School support for PA and community PA resources are associated with MVPA among Chinese school children. School PA facilities appear underutilized among urban schools as evidenced by low levels of MVPA among school children.

Assessment of Human Impacts on Vegetation in Built-up Areas in China Based on AVHRR,MODIS and DMSP_OLS Nighttime Light Data,1992–2010

Since the reform and opening-up program started in 1978,the level of urbanization has increased rapidly in China.Rapid urban expansion and restructuring have had significant impacts on the ecological environment especially within built-up areas.In this study,ArcGIS 10,ENVI 4.5,and Visual FoxPro 6.0 were used to analyze the human impacts on vegetation in the built-up areas of 656Chinese cities from 1992 to 2010.Firstly,an existing algorithm was refined to extract the boundaries of the built-up areas based on the Defense Meteorological Satellite Program Operational Linescan System(DMSP_OLS)nighttime light data.This improved algorithm has the advantages of high accuracy and speed.Secondly,a mathematical model(Human impacts(HI))was constructed to measure the impacts of human factors on vegetation during rapid urbanization based on Advanced Very High Resolution Radiometer(AVHRR)Normalized Difference Vegetation Index(NDVI)and Moderate Resolution Imaging Spectroradiometer(MODIS)NDVI.HI values greater than zero indicate relatively beneficial effects while values less than zero indicate proportionally adverse effects.The results were analyzed from four aspects:the size of cities(metropolises,large cities,medium-sized cities,and small cities),large regions(the eastern,central,western,and northeastern China),administrative divisions of China(provinces,autonomous regions,and municipalities)and vegetation zones(humid and semi-humid forest zone,semi-arid steppe zone,and arid desert zone).Finally,we discussed how human factors impacted on vegetation changes in the built-up areas.We found that urban planning policies and developmental stages impacted on vegetation changes in the built-up areas.The negative human impacts followed an inverted′U′shape,first rising and then falling with increase of urban scales.China′s national policies,social and economic development affected vegetation changes in the built-up areas.The findings can provide a scientific basis for municipal planning departments,a decision-making reference for government,and scientific guidance for sustainable development in China.

Examining Rate of Built-Up Areas on the Vegetation Cover along River Riara Riparian within Kiambu Town, Kenya

Urban river riparian spaces and their natural systems are valuable to urban dwellers;but are increasingly affected and ruined by human activities and in particular, urbanization processes. In this research, land sat and sentinel satellite imagery apt for change detection in vegetation cover, both landsat and sentinel imagery, covering the period between 1970 and 2021 in epochs of 1973, 1984, 1993, 2003, 2015 and 2021 years were used to establish the correlation between vegetation cover and built-up area along River Riara river reserve. The images were analysed to extract the built-up areas along the river reserve, including the buildings, and the rate of human settlements, which influenced vegetation cover. Normalized Difference Built-Up Index (NDBI) and Normalized Difference Vegetation Index (NDVI) were computed using the Short-Wave Infrared (SWIR) and the Near Infra-Red (NIR) bands to show the rate of change over the years. Results indicate NDVI values were high, compared to NDBI values along river Riara in the years 1973 and 1993 implying that there was more vegetation cover then. However, in the year 2021, the NDVI indicated the highest value at 0.88, with the complementary NDBI indicating the highest NDBI value at 0.47. This represents a significant increase in built-up areas since 2015 more than in previous epochs. Either, there was a significant increase in NDBI values, from 0.24 in 1993 to 0.47 in 2021. More so, the R-squared value at 0.80 informed 80% relationship between NDBI and NDVI values indicating a negative correlation.

我国城乡高中一、二年级学生体质健康测试状况的调查研究

背景目前有关高中生体质健康测试成绩的研究以各省、市内局部地区较为多见,多中心大样本量的全域研究甚少。各类学校在普遍开展线上与线下混合式教学时,势必延长了高中生本已较长的静坐时间。这种趋势是否对高中生的体质健康产生一定的影响,亟待开展全域范围的调查研究。目的调查并分析我国七大地区城乡高中一、二年级学生的体质健康测试成绩水平及相关影响因素,探索出高中一、二年级学生的体质健康水平均衡提升的赋能路径。方法采用分层随机整群抽样方法,于2019年1—3月在我国31个省(直辖市、自治区)七大地区(华东、华南、华北、华中、西北、西南、东北)高中学校按照市区县与乡镇村进行分层抽样,然后随机整群分别选取市区县高中学校和乡镇村高中学校各1所,共62所学校42523名在读的高一、高二年级学生进行调研,同时收集学生的体质健康测试成绩数据(BMI反映身体发育水平,肺活量反映身体功能,坐位体前屈反映躯体柔韧度,引体向上、50 m跑、立定跳远反映上下肢爆发力量水平,1 min仰卧起坐反映躯体核心力量水平,800 m跑、1000 m跑反映心肺耐力水平),并运用非参数检验及多元线性回归分析探讨体质健康测试成绩水平的影响因素。结果42523名高中生的中位年龄为16.0(16.0,17.0)岁;男生20074名(47.2%)、女生22449名(52.8%),市县区21725名(51.1%)、镇乡村20798名(48.9%)。七大地区高中生性别、城乡分布比较,差异有统计学意义(P<0.05)。七大地区高中男生各项体质健康测试成绩比较,差异均有统计学意义(P<0.05);各项体质健康测试成绩前三的地区如下:身高(华北>东北>华中)、体质量(东北>华北>华中)、BMI(华中>东北>华北)、肺活量(东北>华中>华南)、50 m跑(华南>华中>华东)、立定跳远(华南>华北>西北)、坐位体前屈(华南>西南>华中)、引体向上(华南>西南>西北)、1000 m跑(华南>华中>西南)。市县区高中男生的肺活量成绩高于镇乡村,50 m跑、立定跳远、坐位体前屈、引体向上、1000 m跑成绩低于镇乡村(P<0.001)。七大地区高中女生各项体质健康测试成绩比较,差异均有统计学意义(P<0.05);各项体质健康测试成绩前三的地区如下:身高(华北>东北>西北)、体质量(东北>华北>西北)、BMI(东北>华北>西北)、肺活量(东北>华南>华中)、50 m跑(华南>华中>华东)、立定跳远(华南>华北>华中)、坐位体前屈(东北>华中>华南)、1 min仰卧起坐(华北>华中>华东=西南)、800 m跑(东北>华中>华南)。市县区高中女生的身高、体质量、BMI成绩高于镇乡村,肺活量、50 m跑、立定跳远、坐位体前屈、1 min仰卧起坐、800 m跑成绩低于镇乡村(P<0.001)。多元线性回归分析结果显示,男生引体向上成绩与BMI、1000 m跑成绩呈负相关,与50 m跑、立定跳远、坐位体前屈成绩呈正相关(P<0.05),坐位体前屈为最主要的影响因素,1000 m跑次之;1000 m跑成绩与BMI、肺活量、引体向上成绩呈负相关,与50 m跑、立定跳远、坐位体前屈成绩呈正相关(P<0.05),引体向上为最主要的影响因素,坐位体前屈次之。女生1 min仰卧起坐成绩与BMI、肺活量、立定跳远、800 m跑成绩呈正相关,与50 m跑、坐位体前屈成绩呈负相关(P<0.05),BMI为最主要的影响因素,坐位体前屈次之;800 m跑成绩与BMI、50 m跑、坐位体前屈成绩呈负相关,与立定跳远、1 min仰卧起坐成绩呈正相关(P<0.05),坐位体前屈为最主要的影响因素,BMI次之。结论我国市县区高中一、二年级男生的身体发育水平与镇乡村相当,但市县区高中一、二年级女生的身体发育水平高于镇乡村女生。市县区高中一、二年级学生的上下肢爆发力量、躯体核心力量、心肺耐力水平均显著低于镇乡村。除身体发育水平以外,华南地区的高中一、二年级男生的体质健康各项测试成绩水平的优势十分明显。

基于抗衰退韧性评价的城市住区体检与“精明更新”研究

聚焦存量提质时期我国庞大规模老旧住区更新面临巨大资金缺口和社会压力的现实背景,针对既有住区更新、住区体检方法“重要素特征,轻系统状态;重目标评价,轻问题诊断”的理论瓶颈,探索建构出以“低度干预,高效增值;未病预防,靶向提升;人本响应,时空统筹”为行动逻辑的城市住区“精明更新”方法。该方法以住区“精明体检、精明诊断、精明治疗”为操作闭环,以物质空间韧性与社会生境韧性两大韧性系统,住房条件、住区环境、设施水平、人口结构、治理水平5类要素及其下辖13项细分指标为评价因子,对城市住区进行动态监测、科学诊断,将其划分为高、中、低韧性等级和物质衰退、社会衰退、风险叠加等衰退类型;并通过监测养护、短板补益、综合干预和空间提质、邻里链接、时空重构等措施,对不同韧性等级、衰退类型住区进行更新时序统筹和问题靶向调节。相关内容以期为我国城市住区更新实践提供方法参考和技术支持。

国家气候观象台多维度观测能力建设及科学研究——以深圳为例

国家气候观象台是中国国家级气象观测的重要节点,发展国家气候观象台的观测能力,并依托其开展有特色的科学研究,有助于推动我国大气科学发展。深圳国家气候观象台是我国珠三角经济圈环境综合观测区唯一的国家级气候观象台,经过20余年的持续不断建设,已具备了城市—郊区的对比监测、气象—环境的联合监测、地面—高空的立体监测和陆地—海洋的协同监测等多方面的监测能力。基于深圳国家气候观象台的观测数据,大气科学领域的学者们已在粤港澳大湾区城市气候、边界层风特性及致灾机理、大气环境与环境气象、气候资源、地闪雷电特征等多个领域开展研究并取得了丰硕的成果,进一步丰富了对这些领域的科学认识。此外,深圳国家气候观象台还支撑了深圳本地的防灾减灾、城市管理、城市规划以及生态文明建设等工作,已逐渐成为发挥气象观测社会效益的典范。

基于城市实体地域的城乡接合部空间界定研究——以广州市为例

当前国内外城乡接合部空间界定研究尚未达成共识,在行政管理实践中也未形成明确的标准,导致了城乡接合部空间治理的现实困境。基于此,文章提出基于城市实体地域的城乡接合部空间界定方法,对广州市进行实证研究。结果表明:1)以自然资源部高精度遥感和土地调查数据准确识别的城市实体地域范围为城乡接合部空间界定测算指标,以明确的行政村、居委会为最小统计单元,可以有效地衔接国土空间规划技术体系;2)采用国内外大多数研究认同的25%~75%理想值与聚类分析法,并以广州市为典型案例进行城乡接合部空间界定阈值的优化与检验,最终确定广州市城乡接合部空间界定合理阈值为10%~75%;3)精准的测算指标、明确的研究单元和可操作性强的界定方法,可以较好地识别出城乡接合部空间,同时也为更深入的空间研究与治理提供支撑。

城市绿地不同林分结构特征对土壤物理性质的影响

科学调整林分结构是解决城市绿地人工林土壤退化的重要途径。研究旨在为城市绿地合理经营提供理论依据。在山西省太原市森林公园中选取油松、榆树和刺槐人工纯林,分别设置20 m×20 m样地并以5 m间距均匀采集土壤样品,基于立木定位和每木检尺计算距土壤采样点不同半径处的林木株数、邻近木平均胸径等林分结构参数,采用Pearson相关和偏最小二乘回归分析法探讨林分结构因子对土壤物理性质的影响。结果表明,不同林分土壤物理性质存在一定差异,榆树林下土壤容重显著低于油松林和刺槐林,而土壤含水量、毛管持水量、毛管孔隙度、饱和持水量高于油松林和刺槐林。林分结构因子与土壤物理性质的相关系数在与立木冠幅均值大小近似的尺度上呈现最大值。通过Pearson相关性分析和偏最小二乘回归分析双重验证得出,榆树林的树高与土壤饱和持水量、毛管持水量、含水量存在极高的正相关性,相较于其他2个树种对改善土壤物理性质表现较优。

城郊融合背景下京津冀中小城镇中心城区地域范围识别及应用研究——以河北省宁晋县为例

中心城区地域范围(以下简称“城区地域范围”)识别是新时代国土空间规划体系建构的前提与基础。在以县城占据主导地位的京津冀地区,绝大多数中小城镇具有“城村交织”“城乡互嵌”的空间特征,面对推进实施以县城为主要引擎和重要载体的新型城镇化战略的发展趋势,科学界定该地区中小城镇中心城区的地域空间,成为开展市县国土空间规划编制工作的第一环节。文章分析了传统土地调查以城镇村属性为“202及202A”用地图斑识别作为城区地域范围的局限性,以河北省宁晋县为例,对比在城镇基数转换、城市体检评估等不同工作思路中确定的城区地域范围的划定情况,提出适用于京津冀地区中小城镇城区地域范围识别的方法和途径,为支撑城镇开发边界优化调整、判断城郊融合类村庄、推进城乡一体化发展提供重要依据。

Dynamics of Urbanization and Its Impact on Land-Use/Land-Cover: A Case Study of Megacity Delhi

The rapid expansion of urban areas due to rise in population and economic growth is increasing additional demand on natural resources thereby causing land-use changes especially in megacities. Therefore, serious problems associated with rapid development such as additional infrastructure, informal settlements, environmental pollution, destruction of ecological structure and scarcity of natural resources has been studied carefully using remote sensing and GIS technologies for a rapidly grown megacity namely, Delhi. The present work evaluates the land use/land cover (LULC) changes and urban expansion in Mega city Delhi and highlights the major impact of rapid urbanization and population growth on the land cover changes which needs immediate attention. The results indicate that the city is expanding towards its peripheral region with the conversion of rural regions in to urban expansions. Built-up area of Delhi witnessed an overall increment from 540.7 km2 to 791.96 km2 or 16.86% of the total city area (1,490 km2 ) during the study period 1997 to 2008 which mainly came from agriculture land, waste land, scrub-land, sandy areas and water bodies. The increment in forest cover of 0.5 % is very small when considering the increment in built up category to 17%. Total area of waterbodies has reduced by 52.9% in a ten year period (58.26 km2 in 1997 to 27.43 km2 in 2008) with shallow waterbodies now having a dismal presence. LULC changes are studied with the urban growth parameters such as population, vehicles, gross state domestic product etc. The results lay emphasis on the concepts of urban planning to be applied such that more consideration is towards the preservation and management of natural land use classes which will increase the quality of life in an urban environment.

Statistical Change Detection in Water Cycle over Two Decades and Assessment of Impact of Urbanization on Surface and Sub-Surface Water Flows

Urbanization is termed as physical transformation of landscapes that alter the natural regime of the environment of its surrounding resulting in further changes in macro as well as micro climate of the region [1]. Urban areas are continually facing problems of water scarcity and urban flash floods. Recent news from IPCC report 2010, CIESIN’s Global Rural Urban Mapping Project [2] and World Water Vol. 7 2007, it is clear that urban land area has doubled and affected the hydrological cycle. The components of hydrological cycle affected are Infiltration, Runoff and Evaporation and the causing components are derived by studies as land use, land cover, water withdrawal and urban developments. Thus water availability, water recharge and water cycle are all destabilized in course or urban development. The paper is an attempt to correlate and identify the periodical changes in urban water cycle, during urbanization of Bhopal City, India, during last twenty years and above. The observations are based on GIS mapping of the study area from 1991 to 2009 using rational method of runoff and recharge calculations and statistical analysis of related built-up areas. Also change in natural course of drainages with the help of GIS imageries which have been detected during twenty years that help to observe the adaptation of natural system to urban course. Also the observations show an interesting relation which can be used for further research and sustainable development [3].

Analysis of the Relationship between Land Surface Temperature and Vegetation and Built-Up Indices in Upper-Hill, Nairobi

Designing “liveable” cities as climate change effects are felt all over the world has become a priority to city authorities as ways are sought to reduce rising temperatures in urban areas. Urban Heat Island (UHI) effect occurs when there is a difference in temperature between rural and urban areas. In urban areas, impervious surfaces absorb heat during the day and release it at night, making urban areas warmer compared to rural areas which cool faster at night. This Urban Heat Island effect is particularly noticeable at night. Noticeable negative effects of Urban Heat Islands include health problems, air pollution, water shortages and higher energy requirements. The main objective of this research paper was to analyze the spatial and temporal relationship between Land Surface Temperature (LST) and Normalized Density Vegetation Index (NDVI) and Built-Up Density Index (BDI) in Upper-Hill, Nairobi Kenya. The changes in land cover would be represented by analyzing the two indices NDVI and BDI. Results showed the greatest increase in temperature within Upper-Hill of up to 3.96&#176C between the years 2015 and 2017. There was also an increase in impervious surfaces as indicated by NDVI and BDI within Upper-Hill and its surroundings. The linear regression results showed a negative correlation between LST and NDVI and a positive correlation with BDI, which is a better predictor of Land Surface Temperature than NDVI. Data sets were analyzed from Landsat imagery for the periods 1987, 2002, 2015 and 2017 to determine changes in land surface temperatures over a 30 year period and it’s relation to land cover changes using indices. Visual comparisons between Temperature differences between the years revealed that temperatures decreased around the urban areas. Minimum and maximum temperatures showed an increase of 1.6&#176C and 3.65&#176C respectively between 1987 and 2017. The comparisons between LST, NDVI and BDI show the results to be significantly different. The use of NDVI and BDI to study changes in land cover due to urbanization, reduces the time taken to manually classify moderate resolution satellite imagery.

Impact of Urbanisation on Land Use/Land Cover in Puducherry City, India

The change of land use plays a major role in the developmental activity of a developing country. Due to rapid growth of urbanisation and dramatic increasing population, the fertile agricultural land has been converted to built-up area with respect to the demand for housing requirement and to the need for basic infrastructure facilities. The quantum of open space and surface water bodies has also been encroached. There has been a rapid growth of population in Puducherry city from 3.48 million in 1991 to 5.44 million in 2011. Hence the conservation of natural resources becomes one of the major challenges especially in small and medium town. This study was conducted to assess the effect of change on land use in urban agglomeration area of Puducherry city for the duration period from 1997 to 2017. There has been an increase in population in Puducherry city mainly attributed to higher scale of migration from adjoining rural areas and medium town for better education, job opportunities and quality life. Hence, it has been strongly recommended for stringent Development Control Regulations to quantify the urban sprawl and manage the impact of urbanisation of land use/land cover in Puducherry city.

Analyzing Urban Expansion and Spatial Growth Patterns in Barahathawa Municipality of Central Tarai Region, Nepal

The rapid transformation of rural settlements into municipalities in Ne­pal has brought significant changes in land use,and urban expansion and growth patterns mostly through the conversion of agricultural land into the built-up area.The issue is studied taking a case of the rapidly growing town,Barahathawa Municipality of Tarai Region of Sarlahi District.After the declaration of the municipality,several new roads have been opened and upgraded;and the municipality is well-connected to the national transportation network.After promulgated the Constitution of Nepal 2015 and functioning the elected local body,the municipality budget has been increased significantly as a result of increasing municipal investment in so­cio-economic and physical infrastructure development and environmental protection which has attracted people,goods,and services creating the zone of influence on the municipality.One of the changes found in the munici­pality is the increasing built-up area and expansion of urban growth through the decreasing agricultural land.Urban growth has been observed taking place around the Barahathawa Bazaar and main roadsides.The built-up area in Barahathawa municipality has remarkably increased by 183percent with the decrease of shrub and agricultural land within 10 years.Implica­tions of such spatial and temporal dynamics have been a core issue of urban planning in most of the newly declared municipalities in Nepal.

基于多维城乡差异化人地特征的城区范围识别方法——面向中国多样本城市的实践探索

研究目的:基于概念辨析与方法演进分析,从城乡差异化人地特征入手,构建指标量化下的城区范围识别方法并应用于107个样本城市进行准确度校验。研究方法:文献资料法、归纳演绎法、实证分析法。研究结果:(1)城区概念中的实体地域认知日益深化,现有多类指标筛选法、遥感影像识别法、大数据与人工智能识别法三类识别方法且具有差异化应用特征;(2)可从人口、土地、产业、环境4个维度选取差异化特征要素并确定指标条件,构建以实体地域为基础的城区范围识别方法;(3)借助影像数据、矢量数据和统计数据,依次通过初步筛选获得城区初始范围,通过图斑功能、连接度、边界核查等判断获得城区实体地域范围,通过图斑占比、市政公用和公共服务设施等分析获得城区范围;(4)在方法准确度校验中,105个样本城市的城区实体地域范围面积与同年度建成区面积平均偏差为21.2%,趋势线斜率为0.825,判定方法有效。研究结论:本方法可应用于全国各区域城市的城区范围识别,未来可在人口指标增补、统计精度提升等方面进行优化并开展镇区、乡村空间识别的延续性研究。

Global mapping of urban built-up areas of year 2014 by combining MODIS multispectral data with VIIRS nighttime light data

An improved methodology for the extraction and mapping of urban built-up areas at a global scale is presented in this study.The Moderate Resolution Imaging Spectroradiometer(MODIS)-based multispectral data were combined with the Visible Infrared Imager Radiometer Suite(VIIRS)-based nighttime light(NTL)data for robust extraction and mapping of urban built-up areas.The MODIS-based newly proposed Urban Built-up Index(UBI)was combined with NTL data,and the resulting Enhanced UBI(EUBI)was used as a single master image for global extraction of urban built-up areas.Due to higher variation of the EUBI with respect to geographical regions,a region-specific threshold approach was used to extract urban built-up areas.This research provided 500-m-resolution global urban built-up map of year 2014.The resulted map was compared with three existing moderate-resolution global maps and one high-resolution map in the United States.The comparative analysis demonstrated finer details of the urban built-up cover estimated by the resultant map.

Underground space use of urban built-up areas in the central city of Nanjing:Insight based on a dynamic population distribution

With the expansion of cities and the emergence of various urban problems,urban underground space has been developed as a solution.In China’s urban transition context,there is a need for the development of underground space in urban built-up areas.In this casestudy of the central city of Nanjing,we used spatial analysis and statistical methods to characterize the underground space use of urban built-up areas from a dynamic spatiotemporal perspective.We first analyzed the relationship between the population distribution and the underground space use of the central city of Nanjing based on a Baidu heat map,which can reflect the real-time population distribution,and then,we explored the spatiotemporal characteristics and spatial structure of the underground space use in urban built-up areas.The analysis results provide a reference for planning to improve and optimize the layout of underground space in the central city of Nanjing and,more generally,for the stock-type planning of underground space in urban built-up areas.

Chinese City Size Ranking: A Comparative Study of the Urban Built-Up Area Based on Remote Sensing Data

Without a clear and unified definition of the urban built-up area, many city rankings by area are inconsistent, giving rise to confusion among the general public and even scholars. This paper summarizes various definitions of the urban built-up area and proposes three definition methods: all urban built-up areas in a municipal administrative area, concentrated contiguous built-up areas, and urban built-up areas in central cities. From the latest Landsat 8 satellite images, the paper obtains the data of urban built-up area in some of China’s big cities and makes a comparative study between the results of the urban built-up areas by the three definition methods and three other common statistical data. It finds that neither the area data nor the ranking is consistent. Finally, it further explores what causes differences in rankings and gives some advice for improving the definition of the urban built-up area.