基于POI数据西安市商业集聚特征分析

商业网点的空间分布特征是城市商业活动的重要体现,研究商业网点的空间分布,有利于了解该地区商业发展现状及趋势.以西安市中心城区为例,基于商业兴趣点(POI)数据和西安市路网数据,运用核密度分析法、最近邻指数法、 Getis-Ord Gi*指数法,分析西安市中心城区商业网点的空间分布特征.结果表明:西安市中心城区呈现出"一轴多核"的商业分布模式,"一轴"指的是西安城市南北中轴线长安路,"多核"包括高新区商圈、小寨商圈、龙首原商圈以及解放路商圈;以路网为单元,对西安中心城区进行网格划分,识别商业街区冷热点分布,其中商业热点分布区域与商业密度中心分布总体一致,呈现出"中心高—外围低"的商业分布模式;各商业类型发展态势不均衡,餐饮类、生活服务类、休闲娱乐类分布范围较广,住宿类、购物类、金融类以及商务类分布范围较为集中.     

Tests of larval retention in a tidally energetic environment reveal the complexity of the spatial structure in herring populations

Dispersion during the larval phase is of central importance in the dynamics of marine fish and invertebrate populations. Rapid transport or dispersion of larvae may contribute to connectivity and mixing, whereas spatial persistence (retention) is hypothesized to favour stock complexity and local subpopulations. Larval retention, while rarely quantified, may be defined in species with protracted spawning by the spatial co‐occurrence of larvae of different sizes or ages. The spatial distributions of larval Atlantic herring (Clupea harengus) were examined from 22 annual autumn surveys (1975–1998) and 9 spring surveys (1975–1984) from the Bay of Fundy, a region with large tides and residual flow. Larvae of all sizes (3–27 mm in length, from hatch to nearly 4 months post‐hatch) were observed each year in two major aggregations; one off southwestern Nova Scotia, and the other in the mid‐inner Bay of Fundy off the northwestern shore of Nova Scotia. Two similar aggregations were evident over 5 months later from 9 spring surveys (1975–1984), despite the residual flow that would have swept the larvae from the region within 1 month. Larval retention was apparent from overlapping centres of mass of different size (=age) classes of larvae, and tested using a size diversity index, based on the co‐occurrence of 1‐mm‐size categories, derived from protracted spawning of several weeks. Geospatial ‘hot spots’ (G_i* statistic) of four size (age) classes were evident at specific stations in the 50–100 m bathymetric zone and not elsewhere. These metrics provide quantitative measures of retention that may be applied to many ichthyoplankton data sets. One of the three main spawning areas collapsed during the study period after a period of intense fishing and failed to rebuild, but there was no substantial change in the location of larval hotspots in subsequent years. While larval retention does not directly relate to each spawning location, larval retention in the Bay of Fundy contributes to the complex ‘metapopulation’ structure of herring stocks in the western Atlantic.     

南极磷虾资源分布热点分析的空间尺度效应

空间尺度是生态学的一个重要研究领域,但少有研究关注空间尺度对生物资源热点分析产生的影响。为了分析不同空间尺度对南极磷虾环南极分布热点的影响,以10年为间隔,将1926—2016年南极磷虾资源密度数据插值为10′×10′、20′×20′、30′×30′、40′×40′、50′×50′、1°×1°、2°×2°、3°×3°、4°×4°、5°×5°这10个空间尺度,利用线性、对数、指数、幂律和多项式函数计算了南极磷虾资源全局密度、磷虾资源热(冷)点区密度与空间尺度之间的关系,分析了热(冷)点区在不同空间尺度下质心与面积的变化。结果显示,南极磷虾资源全局密度的最大值、偏度、峰度、变异系数与空间尺度之间存在显著的比例关系,热点区的最大值、偏度、峰度、Q3、变异系数与空间尺度之间存在显著的比例关系,而冷点区的最大值、平均值、标准差、偏度、峰度、Q3、变异系数与空间尺度之间存在显著的比例关系。热(冷)点区的面积随着空间尺度的增大而增大,其位置受空间尺度变化的影响较大。当空间尺度大于1°×1°时,热(冷)点区的质心偏移严重,故不建议将大于1°×1°的空间尺度用于识别南极磷虾的局部空间格局。