Zhang Lina
Department of Urban and Regional Planning, The Faculty of Spatial Planning, TU Dortmund University, Dortmund, 44149, Germany.
F1000Res. 2021 Aug 4;10:751. doi: 10.12688/f1000research.51483.2. eCollection 2021.
Geographic weights are vital in the floating catchment area (FCA) method of accessibility measurements due to their simulation of spatial barriers in various ways. When modelling population demand, geographical weights with different distance decay coefficients can reflect diverse distance tolerances in facility utilization and could lead to erratic accessibility results. Quantifying accessibility as the sum of weighted supply-demand ratios can alleviate the distance decay coefficient's influence and generate stable geographic patterns. However, the effects of weighted ratios on different FCA models and resources have not been investigated. To identify impacts of weighted ratios on various FCA variants, this study contrasted the accessibility calculated from the sum of ratios (access) and the sum of weighted ratios (access ratios) within three prevalent FCA models: enhanced two-step FCA (E2SFCA), modified two-step FCA (M2SFCA), and three-step FCA (3SFCA). In addition, the accessibilities of various resources evaluate the stability of the weighted ratios' effect. This study therefore examined the accessibilities to primary schools, job opportunities, and major hospitals in Shanghai. Shanghai is a case study that provides lessons on using big data to measure accessibility in metropolitan areas. Geographic weights can not only mitigate the impact of the distance decay coefficients, but can also eliminate model features, which reduces the performance of the M2SFCA's supply decay and the 3SFCA's population demand adjustment in accessibility results. Moreover, weighted ratios tend to overestimate accessibility in marginal communities that lie within fewer catchments, regardless of the resource type. This tendency can lead to an epistemological trap that creates an inaccurate and counter-intuitive perception of resource distribution in a given area. The results identify a gap between the methodological logic and the empirical perception in accessibility measurements. This study concludes that the use of geographic weights needs to be cautious and epistemologically consistent.
地理权重在可达性测量的浮动集水区（FCA）方法中至关重要，因为它们以各种方式模拟空间障碍。在对人口需求进行建模时，具有不同距离衰减系数的地理权重可以反映设施利用中不同的距离容忍度，并可能导致不稳定的可达性结果。将可达性量化为加权供需比之和可以减轻距离衰减系数的影响，并产生稳定的地理模式。然而，加权比在不同FCA模型和资源上的影响尚未得到研究。为了确定加权比对各种FCA变体的影响，本研究对比了三种常见FCA模型（增强型两步FCA（E2SFCA）、改进型两步FCA（M2SFCA）和三步FCA（3SFCA））中从比率之和（可达性）和加权比率之和（可达性比率）计算出的可达性。此外，各种资源的可达性评估了加权比效应的稳定性。因此，本研究考察了上海小学、就业机会和主要医院的可达性。上海是一个案例研究，为利用大数据测量大都市地区的可达性提供了经验教训。地理权重不仅可以减轻距离衰减系数的影响，还可以消除模型特征，这降低了M2SFCA的供应衰减和3SFCA在可达性结果中的人口需求调整性能。此外，无论资源类型如何，加权比往往会高估位于较少集水区内的边缘社区的可达性。这种趋势可能导致一种认识论陷阱，即对给定区域内的资源分布产生不准确且与直觉相反的认知。结果揭示了可达性测量中方法逻辑与实证认知之间的差距。本研究得出结论，地理权重的使用需要谨慎且在认识论上保持一致。
