高斯两步移动搜索法的模型研究——以上海市绿地可达性为例

合理的配置公共服务设施对城市的现代化建设至关重要。空间可达性是度量公共服务设施配置是否合理的方法之一。在诸多的研究方法中,高斯两步移动搜索法由于直观且运算简便,因而得到广泛应用。但该方法也有不足之处,本文运用格网GIS方法,以上海市的绿地空间可达性为例,对两步移动搜索法进行模型方法的改进研究,并对高斯两步移动搜索法和格网化的高斯两步移动搜索法进行对比分析,结果表明：后者可降低空间可达性的误差,提高可达性精度,对上海市绿地空间可达性反映更加真实、客观。如果选择合理的数据将其格网化,该方法也可以用于其他公共服务设施的空间可达性研究。     

广州市医疗设施可达性模型中端点吸引的影响因素检验

引入出租车GPS数据对医疗设施端点特征指标、服务端特征指标、环境要素指标等进行检验,衡量这些指标对医疗设施端点吸引量和主要服务范围的影响作用。结果显示医疗服务利用符合距离衰减规律,1.5 km内人数最多,超过1.5 km,随距离增加出行人数逐渐减少;医疗设施吸引量受医院规模、所在地区人口数量的正向影响,主要服务范围受到所在地区人口数量的负向影响,其他指标影响不显著。     

Does Better Spatial Access Lead to Better Use of Prenatal Care? A Population Study in Georgia

Understanding the effect of spatial accessibility on service utilization is essential to facilitate prenatal care delivery. Previous studies suggest that mothers with better spatial access are more likely to receive adequate prenatal care. Their conclusions, however, are limited by use of small samples and inappropriate spatial accessibility measurements. This article examines the role of spatial accessibility in explaining the variation of prenatal care utilization among 202,377 mothers in Georgia from 2009 to 2011. Specifically, we use geographic information systems and spatial analysis methods to explore the spatial pattern of inadequate prenatal care utilization. A two-transportation-mode, two-step floating catchment area method is used to measure the spatial access to prenatal care by census tract. The effects of spatial accessibility, combined with the influences of demographic, socioeconomic, behavioral, and medical factors, on the adequacy of prenatal care utilization are investigated with statistical models at the individual level. The results show that mothers with better spatial access are less likely to have adequate prenatal care. The inconsistency of this finding with other existing evidence suggests that the effects of spatial accessibility on health service utilization could be complicated and context specific.     

就医空间可达性分析的两步移动搜索法——以江苏省东海县为例

精确评价医疗设施可达性的空间分异样状况是合理配置医疗资源的前提。本文在回顾国内外关于医疗空间可达性研究的基础上, 采用两步移动搜索法, 以江苏省贫困县--东海县为案例, 以行政村和医院为分析单元, 基于迪卡斯特拉算法计算出各村到医院(卫生院)的最短通行时间, 进而分析各村医疗空间可达性分异情况。采用不用服务时间阈值范围进行空间敏感性分析, 综合研判缺医地区分布特点。与传统的医卫人员和人口比值的方法相比, 两步移动搜索法能有效显示县域范围内医疗可达性的空间分异情况。采用较大的时间阈值, 医疗空间可达性分异较为平滑, 采用较小服务阈值则空间分异显著, 缺医范围也较大。东海县医疗空间可达性整体呈单核结构, 并沿主要交通线延伸, 缺医地区多分布于边缘乡镇。提高边缘乡镇的行政村的甲级卫生院等级和乡村道路等级将会改善边缘乡镇的就医可达性。     

交通拥堵对急救医疗服务时空可达性的影响——以广州市为例

时间是急救服务的敏感因素,急救服务设施可达性的时空差异对于评估急救设施的选址及急救服务调度的效率,解决公众急救医疗需求与供给之间的矛盾,辅助政府部门的决策都至关重要。交通拥堵是常见的城市问题,尤其是在城市中心区域更为明显,由于交通拥堵带来的时间滞后对急救服务产生的影响不容忽视。本文通过浮动车GPS大数据,分析交通拥堵对广州市中心城区急救医疗设施时空可达性的影响。结果表明：①在考虑道路实际通行状况的情况下,在交通高峰期,社区的急救医疗服务平均可达时间和最长可达时间分别比采用设计时速计算增加20%和25%。②可达性存在明显的时空差异。急救医疗服务可达性以急救医院为中心,沿着路网向四周呈现衰减趋势。急救医院布局较多、路网密集区域的可达性高,反之则低。交通拥堵对路网密集、行车规则设计复杂以及存在通过性交通流的地区影响显著。③对不同阻抗系数下可达性变化的敏感性分析,发现随着阻抗系数的增大,可达性变化的趋势有所放缓,紧急医疗服务可达性的分异变小;这一变化趋势在交通平峰期表现更为明显。因此,在研究城市中心区域急救医疗服务时,考虑交通拥堵对可达性的影响,需要构建基于实时交通状况的可达性评估模型,合理选择模型参数,优化实时急救医疗服务调度,提升急救服务的效率和质量。     

Enhancing the Two-Step Floating Catchment Area Model for Community Food Access Mapping: Case of the Supplemental Nutrition Assistance Program

In this article, a Gaussian-based two-step floating catchment area (2SFCA) model is applied to evaluate the geographical accessibility to Supplemental Nutrition Assistance Program (SNAP)-authorized retailers. First, the proposed method considers the interaction between the food supply (in terms of categorized benefit redemptions) and demand (in terms of benefit-receiving households). Second, the model is used to visualize food access patterns at the level of refined administrative units (i.e., census block groups). The developed food access metric was compared to the U.S. Department of Agriculture (USDA) Food Access Research Atlas, justifying the validity of this new method for small area estimation. The following are important observations: (1) the choice of catchment size had a considerable impact on the accessibility measure in urban areas (or when small statistical units are used); (2) the 2SFCA measurement had a higher level of correspondence with that of the USDA Atlas at a smaller catchment size for identifying low food access units; and (3) there was no significant inequality regarding SNAP accessibility with respect to different socioeconomic deprivation variables. This new method can better assist the SNAP administration with store authorization on a refined geographic scale. Key Words: food access, inequality, scale, Supplemental Nutrition Assistance Program (SNAP), two-step floating catchment area (2SFCA).     

Inverted Two-Step Floating Catchment Area Method for Measuring Facility Crowdedness

The popular two-step floating catchment area (2SFCA) method has been widely used in the literature to measure spatial accessibility of residents for a service. The 2SFCA method accounts for the ratio between the supply capacity and demand amount of the service as well as the complex spatial interaction between them. This article introduces an inverted two-step floating catchment area (i2SFCA) method that is derived from an extension of the classic Huff model and used to capture the “crowdedness” (scarcity of resource or intensity of competition) for facilities. The method is illustrated and validated by a case study of evaluating hospital inpatient services in Florida. Several possible uses of the measure are also discussed.     

Measuring Potential Access to Primary Healthcare Services: The Influence of Alternative Spatial Representations of Population

Spatial accessibility measures are an important policy tool for managing healthcare provision and reducing health inequality. The two‐step floating catchment area technique, in common with many alternative methodologies, requires that demand‐side population be estimated using spatial interpolation techniques. This article studies the implications of adopting differing spatial representations of population on healthcare accessibility modeling outcomes. Results indicate that a dasymetric model yields lower accessibility scores than a standard pro rata model. More important, the difference is spatially disproportionate, suggesting that the degree of disadvantage experienced in rural areas may be greater than has previously been recognized.     

Bringing Time Back In: A Study on the Influence of Travel Time Variations and Facility Opening Hours on Individual Accessibility

Although recent studies of individual accessibility have used detailed representations of urban street networks, unrealistic measures of travel time based on assumptions about constant travel speeds through the network were often used. Utilizing constant travel times does not allow for daily congestion and assumes that the effects of congestion are uniform throughout the city and affect all people equally. This research measures individual space‐time accessibility in order to show that the incorporation of locally specific travel times within a street network allows a significant increase in the ability to realistically evaluate individual accessibility within cities. The results show that the accessibility of individuals within cities is not homogenous, and neither does access to employment or shopping opportunities vary according to common expectations about urban form and human behavior. Instead, the role of distance in predicting accessibility variations within cities is quite limited. This article also shows that incorporating time into accessibility measures in the form of congestion and business hours leads to additional (and highly spatially uneven) reductions in accessibility, revealing that the temporal dimension is very important to accurately assessing individual accessibility.     

Bringing Time Back In: A Study on the Influence of Travel Time Variations and Facility Opening Hours on Individual Accessibility

Although recent studies of individual accessibility have used detailed representations of urban street networks, unrealistic measures of travel time based on assumptions about constant travel speeds through the network were often used. Utilizing constant travel times does not allow for daily congestion and assumes that the effects of congestion are uniform throughout the city and affect all people equally. This research measures individual space-time accessibility in order to show that the incorporation of locally specific travel times within a street network allows a significant increase in the ability to realistically evaluate individual accessibility within cities. The results show that the accessibility of individuals within cities is not homogenous, and neither does access to employment or shopping opportunities vary according to common expectations about urban form and human behavior. Instead, the role of distance in predicting accessibility variations within cities is quite limited. This article also shows that incorporating time into accessibility measures in the form of congestion and business hours leads to additional (and highly spatially uneven) reductions in accessibility, revealing that the temporal dimension is very important to accurately assessing individual accessibility.     

Modeling Spatial Accessibility of Immigrants to Culturally Diverse Family Physicians

This article uses accessibility as an analytical tool to examine health care access among immigrants in a multicultural urban setting. It applies and improves on two widely used accessibility models—the gravity model and the two-step floating catchment area model—in measuring spatial accessibility by Mainland Chinese immigrants in the Toronto Census Metropolitan Area. Empirical data on physician-seeking behaviors are collected through two rounds of questionnaire surveys. Attention is focused on journey to physician location and utilization of linguistically matched family physicians. Based on the survey data, a two-zone accessibility model is developed by relaxing the travel threshold and distance impedance parameters that are traditionally treated as a constant in the accessibility models. General linear models are used to identify relationships among spatial accessibility, geography, and socioeconomic characteristics of Mainland Chinese immigrants. The results suggest a spatial mismatch in the supply of and demand for culturally sensitive care, and residential location is the primary factor that determines spatial accessibility to family physicians. The article yields important policy implications.     

Measuring spatial accessibility to primary care in rural areas: Improving the effectiveness of the two-step floating catchment area method

Quantifying spatial accessibility in relation to the provision of rural health services has proven difficult. This article critically appraises the two-step floating catchment area (2SFCA) method, a recent solution for measuring primary care service accessibility across rural areas of Victoria, Australia. The 2SFCA method is demonstrated to have two fundamental shortcomings – specifically the use of only one catchment size for all populations, and secondly the assumption that proximity is undifferentiated within a catchment (especially problematic when the catchment is large). Despite its advantages over simple population-to-provider ratios, the 2SFCA method needs to be used with caution.     

Exploring Metropolitan Accessibility and Urban Structure

Location-based assessments of accessibility gauge the attraction of a place relative to other places. These approaches have been used extensively in models of commuting and urban structure. Even though locational accessibility measures are integral to such efforts, they may also be used to explore aspects of urban spatial structure. As such, this paper presents a GIS-based analysis of locational accessibility for a sample of U.S. metropolitan areas. Indices of accessibility based on spatial interaction models are developed for intraurban residential and employment locations. Results show that residential accessibility patterns are similar across cities, taking a concentric pattern where the central urban area is most attractive. However, employment accessibility varies more from city to city; moreover, the areas of highest employment accessibility tend to be decentralized within their respective regions. Overall, location-based accessibility indices are useful for exploring urban form, particularly with respect to issues of urban sprawl. Directions for future research are identified, including linking comparative urban accessibility measures to ongoing work on commuting, the jobs-housing balance, and urban structure.     

Quantifying multi-modal public transit accessibility for large metropolitan areas: a time-dependent reliability modeling approach

The temporal dimensions of public transit accessibility have recently garnered an increasing amount of interest. However, the existing literature on transit accessibility is heavily based on oversimplified assumptions that transit services operate at deterministic speeds using predetermined timetables. These measurements may overestimate transit accessibility, especially for large metropolitan areas where inter- and intra-modal transfers are frequent. To handle travel time uncertainty, a multi-modal transit accessibility modeling approach is proposed to account for realistic variations in travel time and service reliability. The proposed approach is applied to the mapping of transit accessibility in Shenzhen (China), where transit services exhibit significant travel time variations over space and time. Compared to traditional transit accessibility measures, our method has been demonstrated to better capture intrinsic spatial and temporal accessibility variations with complex multi-modal transit networks. Normal distribution of inter-stop travel times and constant travel speed between GPS sampling points are assumed to simply the computation, which we consider to adjust in future studies to better quantify the dynamics of transit accessibility across space and time.     

A comparative analysis of accessibility measures by the two-step floating catchment area (2SFCA) method

The recent decade has witnessed a new wave of development in the place-based accessibility theory, revolving around the two-step floating catchment area (2SFCA) method. The 2SFCA method, initially serving to evaluate the spatial inequity of health care services, has been further applied to other urban planning and facility access issues. Among these applications, different distance decay functions have been incorporated in the thread of model development, but their applicability and limitations have not been thoroughly examined. To this end, the paper has employed a place-based accessibility framework to compare the performance of twenty-four 2SFCA models in a comprehensive manner. Two important conclusions are drawn from this analysis: on a small analysis scale (e.g., community level), the catchment size is the most critical model component; on a large analysis scale (e.g., statewide), the distance decay function is of elevated importance. In sum, this comparative analysis provides the theoretical support necessary to the choice of the catchment size and the distance decay function in the 2SFCA method. Justification of model parameters through empirical evidence (e.g., field surveys about local travel activities) and model validation through sensitivity analysis are needed in future 2SFCA applications for various urban planning, service delivery, and spatial equity scenarios.     

A GIS-based method to identify spatiotemporal gaps in public service delivery

The focus of methodological approaches to identify (public) service deprivation has been predominantly on the shortcomings in the spatial coverage of the transportation system and the urban opportunity landscape. Accessibility is thereby generally modeled as a static concept with little - if any - account for temporal variations in services and transportation provision across the diurnal cycle and week, such as those resulting from opening hours and congestion effects. This paper suggests the use of time-specific measures of service accessibility and demand. The measures are integrated in a GIS-based multi-criteria analysis with the aim to detect spatiotemporal variations in service deprivation. The applicability of the method has been illustrated in a case study about the planning of a mobile government office bus in the city of Ghent (Belgium). It has been shown that the suitability of alternative stop locations for the bus depends on the time interval during which it will be operated.     

Modeling Commuting Patterns in Chicago in a GIS Environment: A Job Accessibility Perspective

Using the newly released Census for Transportation Planning Package (CTPP) 1990, this research utilizes GIS tools to explain intraurban variations of commuting in Chicago at the Traffic Analysis Zone (TAZ) level. While commute times are directly available from the CTPP, commute distances are derived from the shortest time distances through real-world road networks. GIS surface modeling is used to help identify the major employment center (CBD) and other subcenters. The explanations of commute times and distances are attempted by various measures of job accessibility: the jobs-housing balance ratio defined in a floating catchment area, distances from the CBD and subcenters, and a gravity-based index that takes the effects of all jobs into account. These measurements better explain how far people commute than how much time they spend on commuting. The best model explains over 50% of the variation of commuting among 7,835 TAZs. This is a significant improvement over existing literature, which at best explained less than 30 percent.     

GIS-based dynamic modelling and analysis of flash floods considering land-use planning

Flood inundation is a common natural disaster and a growing development challenge for many cities and thousands of small towns around the world. Soil features have frequently altered with the rapid development of urbanised regions, which has led to more frequent and longer duration of flooding in urban flood-prone regions. Thus, this paper presents a geographic information system (GIS)-based methodology for measuring and visualising the effects on urban flash floods generated by land-use changes over time. The measurement is formulated with a time series in order to perform a dynamic analysis. A catchment mesh is introduced into a hydrological model for reflecting the spatial layouts of infrastructure and structures over different construction periods. The Geelong Waurn Ponds campus of Deakin University is then selected as a case study. Based on GIS simulation and mapping technologies, this research illustrates the evolutionary process of flash floods. The paper then describes flood inundation for different built environments and presents a comparison by quantifying the flooding extents for infrastructure and structures. The results reveal that the GIS-based estimation model can examine urban flash floods in different development phases and identify the change of flooding extents in terms of land-use planning. This study will bring benefits to urban planners in raising awareness of flood impact and the approach proposed here could be used for flood mitigation through future urban planning.     

Modeling Commuting Patterns in Chicago in a GIS Environment: A Job Accessibility Perspective

Using the newly released Census for Transportation Planning Package (CTPP) 1990, this research utilizes GIS tools to explain intraurban variations of commuting in Chicago at the Traffic Analysis Zone (TAZ) level. While commute times are directly available from the CTPP, commute distances are derived from the shortest time distances through real‐world road networks. GIS surface modeling is used to help identify the major employment center (CBD) and other subcenters. The explanations of commute times and distances are attempted by various measures of job accessibility: the jobs‐housing balance ratio defined in a floating catchment area, distances from the CBD and subcenters, and a gravity‐based index that takes the effects of all jobs into account. These measurements better explain how far people commute than how much time they spend on commuting. The best model explains over 50% of the variation of commuting among 7,835 TAZs. This is a significant improvement over existing literature, which at best explained less than 30 percent.     

基于改进高斯两步移动搜索法的深圳市公园绿地可达性评价

公园绿地可达性是衡量城市宜居水平的重要指标.针对传统可达性分析多用统计数据开展评估而导致的供需尺度失衡问题,论文以深圳为例,采用公园绿地空间矢量数据和手机信令数据获取供需空间分布,采用高斯两步移动搜索法计算交通小区(TAZ)尺度公园绿地可达性,并结合可达性结果及供需、交通情况聚类,剖析可达性差异化模式及成因.主要结论如...