HALF A CENTURY OF CROPLAND CHANGE*

ABSTRACT. The census concept of total cropland is a better measure of effective agricultural land than is total farmland, which includes extensive areas of woodland owned by farmers. The cropland area of the United States dropped from 478 million acres in 1949 to 431 million acres in 1997, for a net loss of less than 1 million acres, or roughly one‐fifth of 1 percent, per year. In the midwestern agricultural heartland most counties changed less than 5 percent in the half‐century, and more counties gained than lost. The West was a crazy quilt of change, and in the East most counties lost more than 10 percent. Major metropolitan counties lost a few percentage points more than did adjacent areas, but at a lower rate per capita than the nation as a whole. Most of the loss of cropland was in marginal agricultural counties with soils of low inherent fertility and topography unsuited to modern farm machinery. The loss of cropland to suburban encroachment may be cause for intense local concern, but attempts to thwart development cannot be justified on grounds of a net national loss of good cropland.     

大都市区城市扩张过程及形态对比分析——以东京、纽约和上海为例

大都市区化是全球城市化进程中的普遍现象,研究大都市区域城市扩张进程对理解其未来增长趋势、区域可持续发展具有重要意义。大都市区土地扩张及区域间的对比分析,以及都市区发育过程中城市扩张的一般化空间模式还未被深入理解。论文选取东京、纽约和上海3个大都市区,获取1990—2015年间3期Landsat影像数据,使用梯度和格网分析法,采用城市土地密度函数和城市扩张指数,从建设用地数量变化及其时空分布、城市形态变化等方面,多角度对比分析各城市不同阶段建设用地增长的时空差异。结果表明：① 大都市区边界仍在不断扩展,建设用地在研究期内持续增长;20多年间东京、纽约和上海的建设用地面积分别增长了63%、53%和233%;上海一直处于高强度扩张状态,而纽约的城市扩张在后期几近停滞。② 大都市区建设用地密度从中心向外呈圈层递减式分布,城市核心区和边缘区半径的增长最明显;城市形态均趋向于紧凑。③ 新增建设用地时空异质性明显。东京的远郊新城不断建设,纽约一些尚有发展潜力的区域次中心仍在扩张但速率逐渐放缓,上海的核心区外围增长剧烈并逐渐向远城区推进。④ 大都市区域扩张先后经历高速期—缓慢期—停滞期,扩张进程表现为核心区膨胀—次中心及新城建设—逐步形成稳定的多中心结构。     

BIODIVERSITY AND LAND‐USE CHANGE IN THE AMERICAN MOUNTAIN WEST

ABSTRACT. Rural private lands in the Mountain West of the United States are undergoing a profound land‐use conversion, from agriculture to low‐density residential or exurban development, though little scientific study documents the ecological consequences of this change. Nongovernmental conservation organizations are working with ranchers to keep rangeland out of development and in ranching, ostensibly because these organizations believe that biodiversity is better protected on ranches than on exurban developments. We compared plant and wildlife communities across the principal rural land uses in the Mountain West: protection, livestock ranching, and exurban development. Native plant and faunal biodiversity was better maintained on ranches and protected areas than on exurban developments. Exurban developments favored species that were nonnative or adapted to human‐altered environments. The continued conversion of ranches to exurban development suggests a long‐term alteration of the region's natural heritage.     

基于多源数据和深度学习的城市边缘区判定

城市边缘区的定量分析及判定,对城市发展评价和规划,或是城市空间结构研究都具有重要意义。然而现有研究的边缘区判定指标选择过于单一,判定结果过于破碎,城市预设边界、水体及城市绿地对边缘区判定结果干扰大。针对上述问题,从自然、人口、社会经济的视角出发,以遥感影像、人口数据、POI大数据为数据基础,结合深度学习技术,构建基于多源数据和深度学习的城市边缘区判定方法,进行广州市城市边缘区判定及城市结构空间分布特征分析。结果表明：① 此方法能将城市划分为核心区-边缘区-外缘区,判定结果不会受到预设边界范围的影响,且消除了城市内部水体和城市绿地所造成的破碎化;② 城市边缘区与路网耦合良好;③ 广州市的城市核心区空间分布合理。综上所述,此方法能有效检测城市边缘地带,且结果符合实际情况,能为城市规划、政府决策提供参考。     

Darkness on the Edge of Town: Mapping Urban and Peri-Urban Australia Using Nighttime Satellite Imagery

This article explores the use of nighttime satellite imagery for mapping urban and peri-urban areas of Australia. A population-weighted measure of urban sprawl is used to characterize relative levels of sprawl for Australia's urban areas. In addition, the expansive areas of low light surrounding most major metropolitan areas are used to map the urban–bush interface of exurban land use. Our findings suggest that 82 percent of the Australian population lives in urban areas, 15 percent live in peri-urban or exurban areas, and 3 percent live in rural areas. This represents a significantly more concentrated human settlement pattern than presently exists in the United States.     

Urban land expansion and its driving factors of mountain cities in China during 1990–2015

Land expansion of mountain cities in China is not systematically studied yet. This study identified 55 major mountain cities at and above prefecture level, and analyzed the land expansion characteristics and driving forces, based on visually interpreted data from TM images in 1990, 2000, 2010 and 2015. From 1990 to 2015, total built-up land area of the mountain cities increased by 3.87 times, 5.56% per year. The urban land growth was apparently accelerated after 2000, from 4.35% per year during 1990–2000 increased to 6.47% during 2000–2010 and 6.2% during 2010–2015. Compared to the urban population growth, the urban land expansion rate was 44% higher. As a result, the urban land area per capita increased, but it was still within the government control target, and also was much lower than the average of all cities in China. Urban development policy, changes to administrative divisions, GDP and population growth, and road construction were identified as the major driving forces of land expansion. Terrain conditions were not found a relevance to the urban land expansion rate during 1990–2015, but had a significant impact on the layout and shape, and also probably on the urban land efficiency.     

Assessing housing growth when census boundaries change

The US Census provides the primary source of spatially explicit social data, but changing block boundaries complicate analyses of housing growth over time. We compared procedures for reconciling housing density data between 1990 and 2000 census block boundaries in order to assess the sensitivity of analytical methods to estimates of housing growth in Oregon. Estimates of housing growth varied substantially and were sensitive to the method of interpolation. With no processing and areal‐weighted interpolation, more than 35% of the landscape changed; 75–80% of this change was due to decline in housing density. This decline was implausible, however, because housing structures generally persist over time. Based on aggregated boundaries, 11% of the landscape changed, but only 4% experienced a decline in housing density. Nevertheless, the housing density change map was almost twice as coarse spatially as the 2000 housing density data. We also applied a dasymetric approach to redistribute 1990 housing data into 2000 census boundaries under the assumption that the distribution of housing in 2000 reflected the same distribution as in 1990. The dasymetric approach resulted in conservative change estimates at a fine resolution. All methods involved some type of trade‐off (e.g. analytical difficulty, data resolution, magnitude or bias in direction of change). However, our dasymetric procedure is a novel approach for assessing housing growth over changing census boundaries that may be particularly useful because it accounts for the uniquely persistent nature of housing over time.     

北京城市休闲商务区的时空分布特征与成因

城市休闲商务区（Recreational Business District, RBD）作为城市重要的游憩空间,为外来游客和城市居民提供休闲消费的场所,逐渐受到学界和业界重视。目前大多数研究还停留在概念层面,在分类、空间结构、分布规律、分异成因等方面上还缺乏一定的实证和定量研究。结合前人研究经验,重新定义RBD,并依据城市RBD的特征和属性将其分为大型购物中心、休闲商业街、城市休闲区三类。选取1990年、2000年、2014年三个时间截面对北京各类城市RBD点进行统计,采用基尼系数、空间插值、核密度分析、地理探测器等方法,结合ArcGIS软件,对北京城市RBD的时空分布特征和成因进行分析,得出以下结论：① 时序上看,北京城市RBD的数量和规模不断增加,增速变快,不同类型的RBD出现不同幅度的空间扩张;② 北京城市RBD的空间集聚程度不断加强,不同类型的RBD,存在一定的增幅和增速差异;③ 北京城市RBD的整体空间结构呈“单核聚集—双核发展—网状扩散”的发展模式;④ 城市RBD多选址在交通便利、临近旅游景区、居民和游客密度较高、地价相对较高的地区。⑤ 游客密度对各类型的城市RBD规模均有较大影响;对于不同类型的城市RBD,各因素对其规模的影响也有所不同。     

RACIALIZED TOPOGRAPHIES: ALTITUDE AND RACE IN SOUTHERN CITIES*

ABSTRACT. This study examines altitudinal residential segregation by race in 146 cities in the U.S. South. It begins by embedding the topic in recent theorizations of the social construction of nature, the geography of race, and environmental justice. Second, it focuses on how housing markets, particularly in the South, tend to segregate minorities in low‐lying, flood‐prone, and amenity‐poor segments of urban areas. It tests empirically the hypothesis that blacks are disproportionately concentrated in lower‐altitude areas using gis to correlate race and elevation by digital elevation‐model block group within each city in 1990 and 2000. The statistical results confirm the suspected trend. A map of coefficients indicates strong positive associations in cities in the interior South‐where the hypothesis is confirmed‐and an inverse relationship near the coast, where whites dominate higher‐valued coastal properties. Selected city case studies demonstrate these relationships connecting the broad dynamics of racial segregation to the particularities of individual places.     

城市空间增长与人口密度变化之间的关联关系

探究城市空间增长与人口密度变化之间的关联关系是城市可持续发展研究的基础,对制定有效的土地政策、促进城市紧凑发展具有重要意义。选取中国和欧洲23个人口100万以上城市作为研究样本,采用1990年、2000年和2014年3期土地利用数据和人口数据,计算各时段样本城市空间增长速率,建立城市紧凑度指标,并将城市空间增长方式划分为紧凑型、保持型和蔓延型,进一步探讨了样本城市的空间增长特征、人口密度变化特征及两者之间的关系。主要结论为：① 人口密度降低这一现象普遍存在于中国和欧洲城市,中国城市人口密度相对较高且降低速率较快,欧洲城市人口密度相对较低且降低速率较慢;1990—2014年中国城市半径的增长速率明显快于欧洲城市半径的增长速率。城市空间增长速率与人口密度变化速率呈现强负相关关系（Pearson相关系数为-0.693）;② 1990—2000年中欧城市主要以紧凑型方式增长。2000—2014年中国城市主要以蔓延型方式增长,且人口密度随时间下降的速率加快;欧洲城市主要以紧凑型和保持型方式增长,人口密度降低速率减小;③ 紧凑型的空间增长方式并不一定会带来人口密度的升高,但会减缓人口密度下降的速率。中欧城市对比分析表明,城市维持紧凑型空间增长方式,则城市人口密度随时间下降速率减慢;而空间增长方式由紧凑型转为蔓延型,将加剧城市人口密度随时间下降。     

The Spatial Restructuring of Population in Metropolitan Beijing: Toward Polycentricity in the Post-Reform ERA

Based on data from the third (1982), fourth (1990), and fifth (2000) Population Census of China, this research examines the changing patterns of population distribution in the Beijing metropolitan area in the post-reform era. In the mid-1980s, China launched a series of urban land use reforms aimed toward achieving a market economy. A direct impact of these reforms in Beijing was the restructuring of land uses, evidenced by the relocation of central-city residents to the suburbs to make room for commercial development. This residential suburbanization trend emerged during the 1980s and accelerated in the 1990s. Population change rates varied significantly across subdistricts, and variation was much greater in the 1990s than in the 1980s, indicating an increasingly diverse set of growth trajectories across metropolitan Beijing over time. Various population density functions are tested. The population density pattern is best characterized by a monocentric model in 1982, a dual-centered model in 1990, and a seven-centered model in 2000. This transition in Beijing's urban form toward polycentricity is similar to trends in most Western cities.     

北京城区流动人口扩散格局及驱动机制

基于街道/乡镇尺度人口普查数据,利用GIS空间分析和数理统计方法,从规模、占比、密度和集聚度等4个层面分析北京城区流动人口扩散特征,并揭示其驱动机制。研究发现, 2000~2010年北京城区流动人口规模和密度增加,但流动人口占常住总人口比重和流动人口空间集聚度下降,流动人口呈现明显的空间扩散态势。 北京城区流动人口呈“核-边扩散”格局,城市核心区流动人口规模、密度、占比和空间集聚度不断下降,城市边缘区流动人口规模、密度、占比和空间集聚度逐步上升。 北京城区流动人口的“核-边扩散”格局是经济因素的直接推动、城建因素的间接推动、交通因素的硬性诱导、制度因素的软性诱导等共同作用的结果。     

长江三角洲地区城市用地增长的时空特征分析

以Landsat MSS、TM、ETM 卫星影像为主要数据源,利用遥感和GIS 手段,提取了长江三角洲地区5 个时相(1979 年、1990 年、1995 年、2000 年、2005 年) 城市用地信息,分析了城市用地扩展速度、扩展强度、空间结构的变化特征,进而探讨了长江三角洲1979 年以来的城市空间生长过程。结果表明：① 1979 年以来,长江三角洲城市用地增长呈明显的加快趋势,城市用地总体扩展强度也表现为不断提高。不同行政等级城市用地的扩展强度表现为直 辖市> 地级市> 副省级市> 县(县级市)。② 长江三角洲城市用地空间结构的分维和稳定性特征具有一定的波动性。城市用地的空间结构特征与城市用地增长过程和发展阶段具有一定的联系。③ 长江三角洲城市生长表现出“一核二带”、“二核三带”、“四核四带”和“五核五带”的空间轨迹。     

A resurgence in urban living? Trends in residential location patterns of young and older adults since 2000

ABSTRACT

Some have heralded a resurgence of urban living in the U.S., particularly among young adults. Are Americans abandoning suburbs in favor of more urban lifestyles? What is the scope and scale of this urban resurgence? We develop a typology of neighborhoods to analyze the residential location of young and older U.S. adults from 2000 to 2011–15. Census and national travel survey data reveal that suburban population growth continues to outpace that in urban neighborhoods. Although young adults are more likely than older adults to live in urban neighborhoods, recent urban population growth is neither associated with suburban decline, nor being led by young adults. Significant recent population growth in the newest, suburban neighborhoods suggests that greenfield development remains the primary means to increase American housing supply. Shifting metropolitan growth from the suburban fringe would likely require expanding housing supply in urban neighborhoods, and bringing urban amenities to established inner-ring suburbs.     

北京大都市土地开发的乘数效应和增长模式研究

本依据1992－2000年北京地区2000多个土地开发项目统计资料，通过实证对城市土地空间开发的理论模式进行研究。结果表明，城市特定区域的土地开发，表现为乘数效应作用下的逻辑斯蒂增长。根据模型对各环线和扇面模拟的相关系数高达0．95以上。在此基础上，结合北京举办奥运会带来的巨大投资规模，预测北京大市土地开发的趋势。     

长江三角洲地区城市空间扩展研究

城市化是建设用地扩展的主要驱动因素,分析建设用地时空演化格局已成为学者研究城市化过程的重要视角。采用空间自相关等方法,测度了1985年以来长江三角洲地区城市空间扩展的集聚特征并分析其演变过程;并结合格网建设用地密度频率的变化特点,将空间划分为不同的景观梯度地带,以此研究城市空间在不同地带中的扩展特点。研究结果表明,长三角城市空间扩展聚集程度先降后升,城市化区域融合趋势明显,并在城市空间扩展中表现出以上海、南京和苏州等为代表的3种模式,反应了长三角内部不同的经济发展特点。此外,在不同景观梯度下,长三角城市空间扩展表现出典型的阶段性特征。2000年以前在各个景观梯度下城市空间扩展差异较小,表现为较强的拓展性扩展;2000年以后,在城市核心区扩展强度加强,表现为填充式扩展加快。同时,城乡过渡区面积增加迅速,表明随着城市空间扩展的加速,长江三角洲地区城市土地不集约利用现象已较为突出。     

Evolving United States metropolitan land use patterns

We investigate spatial patterns of residential and nonresidential land use for 257 United States metropolitan areas in 1990 and 2000, measured with 14 empirical indices. We find that metropolitan areas became denser during the 1990s but developed in more sprawl-like patterns across all other dimensions, on average. By far, the largest changes in our land use metrics occurred in the realm of employment, which became more prevalent per unit of geographic area, but less spatially concentrated and farther from the historical urban core, on average. Our exploratory factor analyses reveal that four factors summarize land use patterns in both years, and remained relatively stable across the two years: intensity, compactness, mixing, and core-dominance. Mean factor scores vary by metropolitan population, water proximity, type, and Census region. Improved measurement of metropolitan land use patterns can facilitate policy and planning decisions intended to minimize the most egregious aspects of urban sprawl.     

WHEN THE URBAN FRINGE IS NOT SUBURBAN*

Research on the history of suburbs tends to either disregard the fringe of urban development or locate it beyond the city limits. In this article I argue that compounding fringe and suburban development misrepresents the real differences between the two. I then examine the metropolitan regions of three major U.S. cities‐Baltimore, Buffalo, and Saint Louis in 1880 for evidence of how they differed. A consistent difference emerged between the residents of the suburban districts of a city and those of the presumed location of the fringe.     

中国城市建设用地转型阶段及其空间格局

1978年改革开放以来,社会经济快速发展不断改变着中国城市建设用地形态,并在不同区域表现出非均衡的空间差异。基于中国1981—2015年城市建设用地面积和人口数据,综合运用滑动T检验、K密度估计（KDE）和基尼系数等方法,识别中国城市建设用地转型的关键节点,并揭示其时空特征。结果表明：① 中国城市建设用地形态经历了“面积低速扩张—人均用地收缩”（1981—1990年）、“面积中速扩张—人均用地低速上升”（1990—2000年）、“面积快速扩张—人均用地快速上升”（2000—2015年）3个转型阶段。② 1990—2000年和2000—2015年两个转型阶段,面积转型的空间格局演变缓慢,表现出以东部长三角、珠三角为核心的大聚集和中西部以省会城市为中心的小分散格局,而人均用地转型空间格局呈由东部聚集向全国蔓延的演变趋势。③ 1990—2015年,城市建设用地面积的空间非均衡性表现为先逐渐缩小后逐渐扩大的动态演变特征,人均用地的空间非均衡性表现为先逐渐缩小后趋于稳定的演变特征。④ 中国城市建设用地转型符合区域土地利用转型的理论模式,与社会经济发展阶段转变相对应,空间格局演变揭示了国家发展战略由东部优先向区域协调发展转变的现实情况。研究在内容上弥补了土地利用转型阶段定量识别的不足,可为新时代社会经济转型背景下城市建设用地管控工作提供理论和数据依据。     

中国村庄宅基地空心化评价及其影响因素

依托全国范围内村庄宅基地空心化的典型调查数据,分析了不同区域、区位和地形条件下村庄宅基地的空心化程度及其影响因素。研究显示:①调查村庄宅基地的平均空心化率为10.15%,其中东、中、西部区域村庄宅基地的空心化率分别为14.82%、9.11%和7.15%,呈现出由东向西依次递减的格局;②空间上,高空心化率省份主要集中分布在华北和东北地区;③城镇远郊村庄宅基地的空心化率(11.33%)高于城镇近郊村庄(7.81%),山地区村庄宅基地的空心化率(12.24%)高于平原区(9.91%)和丘岗区(5.86%);④村庄宅基地空心化率对于农村非农就业比重和耕地相对稀缺程度较为敏感。在当前背景下,如果能充分利用已有闲置和废弃宅基地,可满足我国未来10～20年新增农村人口的用地需求。