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1.
Geographic masks are techniques used to protect privacy when publishing sensitive data in maps, but are not well adopted among researchers and may be difficult to execute for some GIS users. We developed a client‐side web application called MaskMy.XYZ that makes geographic masking easy to perform. It executes donut geomasking, a well‐known geographic mask, on thousands of points in seconds, and visualizes the original and masked point patterns in an integrated web map for visual comparison. MaskMy.XYZ also features metrics for both privacy protection and information loss, and allows users to rapidly and iteratively adjust masking parameters based on these metrics. The user interface was designed to prioritize usability, and clear documentation has been included to educate users about geographic masks, which is otherwise only found in niche literatures. By developing this application, we hope that geographic masks will be more widely adopted such that privacy is better protected in research. 相似文献
2.
The impact of fires on environment can have adverse effects. To fully understand the synoptic behaviour of fire events, information on the spatial distributions and their pattern are highly important. In this study, we used 9-year (1997–2005) integrated fire count datasets derived from Along Track Scanning Radiometer (ATSR) satellite to geographically map the distribution of fire events in the Madhya Pradesh state, central India. We then used robust spatial metrics to test the spatial pattern of fire events against the hypothesis of complete spatial randomness (CSR). Specifically, we used the index of dispersion, Green's index, in addition to nearest neighbour statistic for testing CSR. Also, quantification of clustering is carried out using Ripley's K-function. To spatially map the fire events, we used Kernel density estimation that relies on bi-variate probability density functions. Results from using different spatial pattern metrics and nearest neighbour statistics suggested relatively high clustering of fire events in the study area. In addition, results from Ripley's K-function suggested the fire events to be clustered at a lag-distance of ～60 mile radius. By converting original fire ignition locations that are based on historical records to continuous density surfaces, the probability of fire events could be mapped effectively using kernel density estimation. As each fire event is the result of certain spatial process including biophysical and anthropogenic attributes, results from this study can provide useful information on fire management at a local district level. Also, the analysis presented in this study illustrates how spatial patterns in the point datasets can be quantified using different dispersion indices, clustering and density estimation techniques. 相似文献
3.
基于GIS方法,对广州市禁摩前和禁摩后两个时间段的抢劫盗窃犯罪案件数据,进行点模式描述和点模式分析。分析结果表明:禁摩前后广州市抢劫盗窃犯罪的案发地点在空间位置和空间范围上发生了很大变化。空间位置整体向东北方向移动,空间范围进一步扩张,由禁摩前的东西走向变为向西北和东南两个方向延伸;同时,禁摩后的空间聚集程度也有所降低。这些变化都进一步说明了,新时期下,这类犯罪呈现出了新的时空变化特征。 相似文献
4.
本设计主要包括以下几个方面:一是点云数据分幅管理、建立空间索引。三维激光扫描系统获取的点云数据量大,如果直接在所有的点云数据中进行运算,那么运算效率会比较低下,且一般电脑无法处理如此大的数据。因此,必须先对原始大点云分幅处理、建立空间索引,按一定的规律形成计算机可方便处理的小文件,提高运算效率。二是整理断面数据,把断面设计信息按一定的格式整理。三是求解断面的方位、参数等信息,判断每一个横断面所经过的图幅,这一运算过程直接影响到整体效果。四是利用点云数据提取断面点。 相似文献
5.
Population at risk of crime varies due to the characteristics of a population as well as the crime generator and attractor places where crime is located. This establishes different crime opportunities for different crimes. However, there are very few efforts of modeling structures that derive spatiotemporal population models to allow accurate assessment of population exposure to crime. This study develops population models to depict the spatial distribution of people who have a heightened crime risk for burglaries and robberies. The data used in the study include: Census data as source data for the existing population, Twitter geo-located data, and locations of schools as ancillary data to redistribute the source data more accurately in the space, and finally gridded population and crime data to evaluate the derived population models. To create the models, a density-weighted areal interpolation technique was used that disaggregates the source data in smaller spatial units considering the spatial distribution of the ancillary data. The models were evaluated with validation data that assess the interpolation error and spatial statistics that examine their relationship with the crime types. Our approach derived population models of a finer resolution that can assist in more precise spatial crime analyses and also provide accurate information about crime rates to the public. 相似文献
6.
空间点模式是一个2维离散点集,点集中的每一个元素代表地球表面一个点状目标的空间位置。当2维离散点集具有集聚特征时,称其为集聚型空间点模式,它与空间聚类、制图综合和空间分析的许多具体应用紧密相关。如何提取集聚型空间点模式的结构信息(集聚子群的个数和对应的集聚中心)是其中尚未彻底解决的问题。作者以几何概率为理论基础,提出测度正方形区域内2维离散点集分布特征的H函数并推导其解析表达式,运用H函数设计和实现了集聚型2维离散点集结构信息提取的通用算法。利用该算法处理一个由居民地坐标数据得到的具有集聚特征的空间点模式,提取出其结构信息并进行可视表达。分别以该空间点模式中的各离散点为顶点和发生元生成Delaunay三角网和Voronoi图,在Delaunay三角网中保留面积最小的前1/10、前1/100三角形的顶点,在Voronoi图中保留面积最小的前1/10、前1/100邻近多边形的发生元,将可视表达的点集结构信息分别与依据Delaunay三角网和Voronoi图得到的结果进行对比分析。结果表明,运用H函数能够有效地提取出集聚型空间点模式的全局性结构信息,而Delaunay三角网和Voronoi图虽然能够反映其局部密度,但在提取全局结构信息时存在局限性。 相似文献
7.
随着环境问题的日益凸显及公众对环境问题的日益关注,如何将污染分布及发生规律、环境质量状况及变化趋势以科学、准确、直观的方式进行展示并以浅显易懂的方式传递给广大公众,是摆在环境管理者面前的一个问题.本文提出了环境监测信息空间表征定义,并介绍了基于GIS、大数据技术的环境监测信息空间表征的主要形式,包括:①点数据的空间表征;②线数据的空间表征;③面数据的空间表征;④三维可视化空间表征;⑤随时间变化的空间信息表征,以及各空间表征方法在环境监测中的应用. 相似文献
8.
通过空间同位模式挖掘可发现频繁发生在邻近位置的事件集合,为揭示地理现象间的共生规律提供重要的决策支持。由于空间同位模式存在空间异质性问题,已有方法不能很好地探测出空间同位模式分布的相近性区域。为此,本文从地理属性的相近性方向探测同位模式的分布区域,提出了基于粗糙集的局部空间同位模式挖掘方法。首先,从全局视角提取不频繁的空间同位模式作为候选的局部空间同位模式;然后,对候选同位模式的实例位置进行处理,将其分布的热点区域属性作为粗糙数据集,借助粗糙集探测局部空间同位模式自然的分布区域;最后,度量在这些局部区域的频繁程度,生成所有频繁的局部空间同位模式。通过试验与应用发现,该方法不仅可以探测局部空间同位模式分布的相近性区域,还能反映同位模式分布区域的地理属性信息。 相似文献
9.
Mohammad Awrangjeb Mehdi Ravanbakhsh Clive S. Fraser 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(5):457-467
This paper presents an automatic building detection technique using LIDAR data and multispectral imagery. Two masks are obtained from the LIDAR data: a ‘primary building mask’ and a ‘secondary building mask’. The primary building mask indicates the void areas where the laser does not reach below a certain height threshold. The secondary building mask indicates the filled areas, from where the laser reflects, above the same threshold. Line segments are extracted from around the void areas in the primary building mask. Line segments around trees are removed using the normalized difference vegetation index derived from the orthorectified multispectral images. The initial building positions are obtained based on the remaining line segments. The complete buildings are detected from their initial positions using the two masks and multispectral images in the YIQ colour system. It is experimentally shown that the proposed technique can successfully detect urban residential buildings, when assessed in terms of 15 indices including completeness, correctness and quality. 相似文献
10.
Parvaneh Nowbakht Lilian O'Sullivan David P. Wall Paul Holloway 《Transactions in GIS》2023,27(1):84-104
Geoprivacy protection is a significant concern when sharing data. To support sustainable land management by leveraging existing agricultural data, research is needed to identify how the polygon nature of static field parcels can be obfuscated to allow data sharing among individuals and organizations. In this study, five adaptive polygon-based obfuscation methods including PN*Rand, PDonut-k, PDensity-k, PAHilb, and PDonut_AHilb methods were developed and applied on the Irish Nutrient Management Planning Online (NMP Online) agricultural dataset. The polygon-based obfuscation methods introduced in this study were designed with the consideration of properties of spatial polygon objects including the spatial coordinates, shape and size of the polygon, topology, and spatial relationship between adjacent polygons that can be used to identify real-world objects. These methods were developed to guarantee that there is no false-identification and non-unique obfuscation which is important for static polygon objects in terms of accuracy and privacy protection. Qualitative approaches were developed to identify the optimal values of inner and outer radii of donut shape based on k-anonymity satisfaction and subsequently obtain the optimal value of k-anonymity. Several evaluation methods were implemented to compare the methods performance. Density-based methods particularly PDonut-AHilb provide the best trade-off between field parcel confidentiality and spatial pattern preservation and should be considered for researchers and practitioners obfuscating polygon data. 相似文献
11.
Despite their increasing popularity in human mobility studies, few studies have investigated the geo‐spatial quality of GPS‐enabled mobile phone data in which phone location is determined by special queries designed to collect location data with predetermined sampling intervals (hereafter “active mobile phone data”). We focus on two key issues in active mobile phone data—systematic gaps in tracking records and positioning uncertainty—and investigate their effects on human mobility pattern analyses. To address gaps in records, we develop an imputation strategy that utilizes local environment information, such as parcel boundaries, and recording time intervals. We evaluate the performance of the proposed imputation strategy by comparing raw versus imputed data with participants’ online survey responses. The results indicate that imputed data are superior to raw data in identifying individuals’ frequently visited places on a weekly basis. To assess the location accuracy of active mobile phone data, we investigate the spatial and temporal patterns of the positional uncertainty of each record and examine via Monte Carlo simulation how inaccurate location information might affect human mobility pattern indicators. Results suggest that the level of uncertainty varies as a function of time of day and the type of land use at which the position was determined, both of which are closely related to the location technology used to determine the location. Our study highlights the importance of understanding and addressing limitations of mobile phone derived positioning data prior to their use in human mobility studies. 相似文献
12.
机载LiDAR数据能够准确提供对象的三维空间位置信息,无人机高分辨影像具备丰富的色彩信息与纹理信息,综合两种数据的优点,可进行数据集成融合。针对山区普遍存在的分布广泛的植被覆盖类型基质景观,本文通过构建可见光植被指数（VDVI）融合光谱信息点云数据,进行典型植被特征提取的研究。为了验证该方法提取信息的准确度,分别构建了3种数据源并依次进行山区地表植被提取试验。对试验结果定性定量分析表明,融合光谱点云数据的植被覆被率为56.8%,较另外两种数据类型的植被覆被率更加接近参考值（58.2%）,可信度相对较高,效果更好,植被图斑轮廓更加清晰,更适用于目标对象植被特征提取,使融合影像信息的点云数据分类优势得以体现,证实了该方法面向山区植被特征提取的可行性。 相似文献
13.
This article studies Bayesian hierarchical spatial modelling that monitors the changes of residual spatial pattern (structure) of the outcome variable for exploring unknown risk factors in small‐area analysis. Spatially structured random effects (SRE) and unstructured random effects (URE) terms added to the conventional logistic regression model take into account overdispersion and residual spatial structure, which if unaccounted for could cause incorrect identification of risk factors. Mapping and/or calculating the ratio of random effects that are spatially‐structured monitor the extent of residual spatial structure. The monitoring provides insights into identification of unknown covariates that have similar spatial structures to those of SRE. Adding such covariates to the model has the potential to diminish the residual spatial structure, until possibly all or most of the spatial structure can be explained. Risk factors identified are the added covariates that have statistically significant regression coefficients. We apply the methods to the analysis of domestic burglaries in Cambridgeshire, England. Small‐area analysis of crime where data often display apparent spatial structure would particularly benefit from the methodologies. We discuss the methodologies, their relevancy in our analysis of domestic burglaries, their limitations, and possible paths for future research. 相似文献
14.
Evaluating Local Non-Stationarity when Considering the Spatial Variation of Large-scale Autocorrelation 总被引：1，自引：0，他引：1
Multi‐scale effects of spatial autocorrelation may be present in datasets. Given the importance of detecting local non‐stationarity in many theoretical as well as applied studies, it is necessary to “remove” the impact of large‐scale autocorrelation before common techniques for local pattern analysis are applied. It is proposed in this paper to employ the regionalized range to define spatially varying sub‐regions within which the impact of large‐scale autocorrelation is minimized and the local patterns can be investigated. A case study is conducted on crime data to detect crime hot spots and cold spots in San Antonio, Texas. The results confirm the necessity of treating the non‐stationarity of large‐scale spatial autocorrelation prior to any action aiming at detecting local autocorrelation. 相似文献
15.
地图信息的拓扑检索 总被引：2，自引：1，他引：2
毋河海 《武汉大学学报(信息科学版)》1986,(3)
从本质上看,地图数据处理是一种拓扑变换,即在连续变形(处理)中要保持数据中所内函的不变性(结构特征)。当数据处理系统由拓扑关系所充实与制导时,其智能程度就大为增强,可使其由线性处理演变为非线性处理(关联处理)。根据物体间邻接与关联的强烈程度,可把拓扑关系分为两大类:确定型与模糊型。前者原则上用显式表示,后者则宜用隐式表示。两种表示方式作了简要的对比,並强调隐式结构有着经济性与灵活性的主要优点。同时还强调指出,在建库过程中拓扑信息的人工输入应趋于最少。地理信息的检索可分为两类:常规检索与拓扑检索。对于前者,检索的依据是物体本身的标志,如定性检索与定位检索;而对于后者,检索的依据是物体集合之间的空间关系(如邻接关系、关联关系和包含关系)。实现以常规检索为基础的间接拓扑检索,其实质就是用程序的手段把隐含在数据结构中的所求的拓扑关系借助于两个倒排文件(标题索引与栅格索引)予以显式化。文末介绍了三种典型的间接拓扑检索:基于点集合的拓扑检索,基于线集合的拓扑检索和基于面集合的拓扑检索。 相似文献
16.
Geomasking sensitive health data and privacy protection: an evaluation using an E911 database 总被引：2，自引：0，他引：2
Allshouse WB Fitch MK Hampton KH Gesink DC Doherty IA Leone PA Serre ML Miller WC 《国际地球制图》2010,25(6):443-452
Geomasking is used to provide privacy protection for individual address information while maintaining spatial resolution for mapping purposes. Donut geomasking and other random perturbation geomasking algorithms rely on the assumption of a homogeneously distributed population to calculate displacement distances, leading to possible under-protection of individuals when this condition is not met. Using household data from 2007, we evaluated the performance of donut geomasking in Orange County, North Carolina. We calculated the estimated k-anonymity for every household based on the assumption of uniform household distribution. We then determined the actual k-anonymity by revealing household locations contained in the county E911 database. Census block groups in mixed-use areas with high population distribution heterogeneity were the most likely to have privacy protection below selected criteria. For heterogeneous populations, we suggest tripling the minimum displacement area in the donut to protect privacy with a less than 1% error rate. 相似文献
17.
Network Density and the Delimitation of Urban Areas 总被引：3，自引：0，他引：3
Giuseppe Borruso 《Transactions in GIS》2003,7(2):177-191
This paper examines network analysis for urban areas. The research is focused on the problem of definition and visualisation of network geography and network spaces at different scales. The urban scale of analysis is examined and different spatial indices are considered. The built environment of the city is considered as a reference environment for a road network density index. The latter is implemented in order to study the spatial interactions between network phenomena and spaces and to provide further elements for the analysis of urban shape. The study is focused in particular on understanding spatial patterns drawn by networks and in helping with the delimitation of city centres. Different approaches are used to obtain the two indices: a grid–based analysis and a spatial density estimator based on Kernel Density Estimation. The two methodologies are analysed and compared using point data for the urban road network junctions and street numbers as house location identifiers in the Trieste (Italy) Municipality area. The density analysis is also used on road network junctions' data for the city of Swindon (UK) in order to test the methodology on a different urban area. 相似文献
18.
自交叉双边滤波的极化SAR数据相干斑抑制 总被引：1，自引：1，他引：0
相干斑抑制是极化SAR数据预处理的关键步骤。双边滤波是一种空域和值域滤波相结合的优秀边缘保持滤波算法。针对双边滤波在抑制极化SAR数据相干斑的不足,该文将改进的交叉双边滤波引入到极化SAR数据降噪领域,加入散射机制测度来扩展原权重核,根据SPAN图像的局域变差系数自动调整空间方差系数,利用参考图像来度量灰度值和散射机制相似性。实验结果表明:本文方法较经典滤波算法有更强的噪声平滑能力和更好的细节信息保持能力,在保持原数据极化散射信息方面也表现出良好的性能,这为基于极化SAR数据的后续应用提供了支持。 相似文献
19.
A key concern in crime analysis is the “hidden crime” problem. Crime events unaccounted for in police records limit the external validity of official statistics and, more importantly, hinder the ability of the police to manage crime and utilize their resources effectively. The problem is exacerbated in proactive initiatives aimed at curbing violence through hotspot policing, where inaccuracies and imprecision, or, worse, no data at all, diminish prevention efforts. Previous studies have sought to overcome the data problem by juxtaposing police records with ambulance data on assault callouts and have found profound disparities. Specifically, researchers matched “crime hotspots” with “ambulance hotspots” (rather than individual events) because patient confidentiality considerations have prevented health professionals from sharing subject-level data with the police. However, health services can safely share spatial data on wider areas that do not disclose personal information. We build on this line of inquiry by analyzing data from the Thames Valley, United Kingdom, and observing spatial hotspots of different sizes. The results demonstrate that while the police and ambulance services attend to the same communities and similar types of facilities, the police are “blinded” to the location of nearly 8 out of 10 assaults. The incongruency is shown even with severe assaults, but to a lesser extent. We then simulate the reduction in injuries if the police had access to health data at different spatial levels and show that even under the most conservative set of assumptions, such an approach can prevent between 113 and 116 violent injuries each year that might otherwise require hospitalization. 相似文献
20.
支持批量操作的空间索引中,空间数据的分解粒度、局部更新操作的整体影响处理是两个主要难点。本文基于空间分布模式分析,提出了一种空间索引——Pattern-tree。针对批量操作的粒度问题,设计了一种基于空间分布模式探测的空间划分方法,采用一种自上而下与自下而上相结合的索引树构建算法;针对局部插入操作对索引树的整体影响与索引树的调整问题,提出了一种基于空间分布模式变化检测的索引更新方法。试验表明,本文所提出的空间索引结构比STLT、GBI以及SCB等方法具有更高的构建与窗口查询效率。 相似文献