A Review of: “Geographic Information Systems for Geoscientists—Modelling with GIS”

Distances from points to closest shorelines in a given direction are used, for example, in some models for estimating wave exposure. Such distances, also called fetch lengths, can be determined using standard geographic information systems. However, performance may be a problem if these distances are required for a great number of study points. Two new algorithms for determining fetch lengths for study points in the same directions are presented in this paper. It is assumed that the two‐dimensional map is stored in vector format, i.e. shorelines of islands and mainland are stored as polygons. The first algorithm works on a set of undirected line segments derived from the shoreline polygons. The other works on a raster representation of the map. The algorithm saves memory by postponing the rasterisation until necessary. Both of the new algorithms have superior efficiency to a previously reported algorithm when the number of study points is large.     

A new algorithm for distance cartogram construction

A distance cartogram is a diagram that visualizes the proximity indices between points in a network, such as time–distances between cities. The Euclidean distances between the points on the distance cartogram represent the given proximity indices. This is a useful visualization tool for the level of service of transport, e.g. difference in the level of service between regions or points in a network and its improvement in the course of time. The two previously proposed methods—multidimensional scaling (MDS) and network time–space mapping—have certain advantages and disadvantages. However, we observe that these methods are essentially the same, and the merits of both these methods can be combined to formulate a generalized solution. In this study, we first formulate the time–space mapping problem, which includes the key features of both of the above stated methods, and propose a generalized solution. We then apply this solution to the time–distances of Japan's railway networks to confirm its applicability.     

A note on the strains at a distance from an ellipsoidal inhomogeneity

Summary. Eshelby discusses the problem of how the presence of an ellipsoidal inhomogeneity in an otherwise homogeneous isotropic elastic medium disturbs an applied strain field which is uniform at large distances. He gives solutions for the strain field due to the inhomogeneity for points immediately adjacent to the inhomogeneity and for points at great distances from it. In this note we solve his equations to give the strain field at intermediate distances from the inhomogeneity. These solutions may be useful in practice for interpreting strain measurements made near open fissures or in regions of jointed or fractured rock.     

A density-based approach for detecting network-constrained clusters in spatial point events

Existing spatial clustering methods primarily focus on points distributed in planar space. However, occurrence locations and background processes of most human mobility events within cities are constrained by the road network space. Here we describe a density-based clustering approach for objectively detecting clusters in network-constrained point events. First, the network-constrained Delaunay triangulation is constructed to facilitate the measurement of network distances between points. Then, a combination of network kernel density estimation and potential entropy is executed to determine the optimal neighbourhood size. Furthermore, all network-constrained events are tested under a null hypothesis to statistically identify core points with significantly high densities. Finally, spatial clusters can be formed by expanding from the identified core points. Experimental comparisons performed on the origin and destination points of taxis in Beijing demonstrate that the proposed method can ascertain network-constrained clusters precisely and significantly. The resulting time-dependent patterns of clusters will be informative for taxi route selections in the future.     

Automatic selection of weights for GIS-based multicriteria decision analysis: site selection of transmission towers as a case study

Transmission line (TL) siting consists of finding suitable land to build transmission towers. This is just one of the numerous complex geographical problems often solved using GIS-based multicriteria decision analysis (MCDA), which is a set of techniques that weight several geographical features to identify suitable locations. This technique is mostly employed using expert knowledge to identify the correct set of weights; thus adding a certain amount of subjectivity to the analysis, meaning that for the same problem if we change the experts involved, we may reach different results.This research is a first attempt to try and solve this issue. We employed a statistical analysis to quantitatively calculate these weights and we tested our method on a case study about transmission line siting in Switzerland. We compared the distances between each sample in our dataset, in this case study these are location of transmission towers, with each geographical feature, e.g. distance from water features. Then we calculate the same distances but for random points, sampled throughout the study area. The reasoning behind this method is that if samples present a distance from a geographic feature statistically different from the random, it means that the feature played an important role in dictating the location of the sample. In this case for instance, high-voltage transmission towers are purposely built as far away as possible from urban areas. Random points are on the contrary by definition sampled without any constraint. Therefore, when comparing the two datasets, we should find that transmission towers have a larger average distance from urban areas than random points. This allows us to determine that this criterion (i.e. distance from urban centers) is important for planning new TL.The results indicate that this method can successfully weight and rank the most important criteria to be considered for an MCDA analysis, in line with weights proposed in the literature. The advantage of the proposed technique is that it completely excludes human factors, thus potentially increasing the social acceptance of the MCDA results.     

A New Method for Finding Geographic Centers,with Application to U.S. States

The geographic center of a region is a fundamental geographic concept, and yet there is no commonly accepted method for its determination. This article discusses some of its history as well as its definition and calculation, and a new method for its calculation is suggested. The new method minimizes the sum of squared great circle distances from all points in the region to the center. This entails (1) projecting regional boundary points using an azimuthal equidistant projection, (2) finding the geographic center of the projected two-dimensional region, and (3) then transforming this location back to a latitude and longitude. This new approach is used to find the geographic center of the contiguous United States and to provide a new list of the geographic centers for U.S. states. This list improves on the widely used but inaccurate list published by the United States Geological Survey in 1923.     

Why GPS makes distances bigger than they are

Global navigation satellite systems such as the Global Positioning System (GPS) is one of the most important sensors for movement analysis. GPS is widely used to record the trajectories of vehicles, animals and human beings. However, all GPS movement data are affected by both measurement and interpolation errors. In this article we show that measurement error causes a systematic bias in distances recorded with a GPS; the distance between two points recorded with a GPS is – on average – bigger than the true distance between these points. This systematic ‘overestimation of distance’ becomes relevant if the influence of interpolation error can be neglected, which in practice is the case for movement sampled at high frequencies. We provide a mathematical explanation of this phenomenon and illustrate that it functionally depends on the autocorrelation of GPS measurement error (C). We argue that C can be interpreted as a quality measure for movement data recorded with a GPS. If there is a strong autocorrelation between any two consecutive position estimates, they have very similar error. This error cancels out when average speed, distance or direction is calculated along the trajectory. Based on our theoretical findings we introduce a novel approach to determine C in real-world GPS movement data sampled at high frequencies. We apply our approach to pedestrian trajectories and car trajectories. We found that the measurement error in the data was strongly spatially and temporally autocorrelated and give a quality estimate of the data. Most importantly, our findings are not limited to GPS alone. The systematic bias and its implications are bound to occur in any movement data collected with absolute positioning if interpolation error can be neglected.     

Travel From Home: An Economic Geography of Commuting Distances in Montreal

The question of how home and workplace are linked through commuting is at the heart of much recent work on metropolitan areas. However, the emphasis tends to be either on spatial-economic models or on the impact of empirically measured individual, household, neighborhood, and transport mode characteristics; relatively little work has focused on job characteristics and place of employment as they relate to travel to work. In this article, I investigate whether people travel different distances to access different types of job location, with particular attention to the different distances traveled by men and women. My points of reference are the major employment centers (poles) in the Montreal region. After controlling for a wide range of explanations that may account for different travel distances, I conclude that differences in commuting length between different places of work are, by and large, independent of possible explanatory factors such as residential location, economic sector, occupation, income, and participation in household earnings—some places of work generate longer commutes than others. Men and women behave differently in relation to these places: women will travel farther to access jobs in centers whereas men will not; and despite their shorter average overall commutes, women travel farther than men to reach jobs in the CBD. This suggests, at the metropolitan scale, that each job location may have its own local culture or "milieu," and that men and women react differently to them.     

Magnitude studies from ultra-long-period records

Summary. Records from the ultra-long-period seismometer at UCLA were used for finding magnitude formulas valid at longer periods, longer distances and greater depths of focus than the formulas used routinely. For Rayleigh waves from shallow focus events M = log( A/T )+ [1.66–0.9 log(T/20)] logΔ+ 13.3 +0.65 +2.9 log(T/20)] was found to be consistent with the data over a wide range of periods and distances. The same formula, with only a small change, was found to be applicable also for deep focus events, down to a depth of over 600 km. A preliminary formula for long-period body-wave magnitudes was found as well.     

A CO-ORDINATE SYSTEM FOR STUDYING INTERACTIONS IN THE PRIMARY CHRISTALLER LATTICE*

The co-ordinate system (x, y) for the triangular Christaller lattice is generalized by the addition of a third, dependent, z-axis. The extended system yields the lattice distances between lattice points, whereas the original system yields only the plane Euclidean distance.     

A cost path and network analysis methodology to calculate distances along a complex river network in the Peruvian Amazon

Distance is a key variable in explicating environmental, social, and economic conditions and in defining spatial and temporal patterns. Prior research has primarily focused on using simple to complex algorithms for calculating distances along road networks. In contrast, few algorithms are available for distance calculations along fluvial networks which are often more erratic, divergent and transient than road networks. Fluvial transportation is relied upon worldwide, particularly in developing regions, where communities use river networks for transportation, access to natural resources and for trade and commerce. This paper presents a methodology developed for mapping complex fluvial networks for travel distance analysis. The methodology was applied in four major river basins in western Amazonia over some 35,000 km of river length and incorporating 919 communities as origins/destinations. A cost path and network analysis methodology was created using vector and raster datasets in a Geographic Information System (GIS) to assess interactions among communities and the distances traveled by river to reach district capitals, major urban centres and marketplaces. An accuracy assessment using distance values calculated from a previous study using a different methodological approach in the region as well as Google Earth Pro, found a high degree of concordance for distance calculations. Our methodology creates a very flexible approach for complex river systems that can be use to calculate river distances in an adaptive and efficient manner and that can be use in other regions of the world where rural communities must rely on rivers for transportation.     

Critical distances: Comparing measures of spatial accessibility in the riverine landscapes of Peruvian Amazonia

Quantitative measures of accessibility are increasingly used in land cover change modeling and in assessing human pressure on the environment. In riverine Amazonia the significance of physical accessibility for biodiversity, land use patterns and economic livelihoods is widely acknowledged, but attempts to quantify accessibility in practice have been few in number. In this study we compare different distance- and frequency-based measures of spatial accessibility and develop a quantitative model of accessibility patterns for the north-eastern Peruvian Amazonia where rivers form the core of the transportation network. We model accessibility between the rural areas of the Loreto region and the capital city of Iquitos, using different distance algorithms in a geographic information system, and complement the distance model with information on river boat frequencies and transport capacities. Patterns of accessibility are visualized in terms of potential production zones for different types of agricultural and non-timber forest products.This study demonstrates how results from different accessibility measures vary considerably. The mean Euclidean distance to Iquitos is almost 270 km, the mean network distance nearly 760 km and the mean travel time 70 h. Observed network distances from validation points to Iquitos are on average 1.6 times longer than Euclidean distances, and for the whole study area, the average ratio between modeled network distances and Euclidean distances is 3.1. The correlation between network distances and time distances is very strong, but time distances are relatively shorter along the major channels where boat traffic is considerably faster than along narrow, tightly meandering rivers. Measures of boat frequency and transport capacity show that availability of transport possibilities is highly varying across the region. These measures provide insights into the ’thickness’ of trade, indicating the level of market integration for riverine settlements. We conclude that quantifying accessibility in an environment like Peruvian Amazonia requires measures that take into account the spatial structure and dynamic nature of the riverine transportation network. Time as a unit of distance provides the most relevant measure of accessibility in the Amazonian context, where many human actions and traditional livelihoods are controlled by travel times between the regional core and the hinterland.     

On the focusing of seismic body waves at the epicentre's antipode

Summary. This note reports on the remarkable focusing of seismic body waves at or near the antipode (Δ= 180°) of an earthquake's epicentre. The particular seismic velocity structure and sphericity of the Earth cause body-wave phases such as P (diff), PKP, PP, PPP, PcPPKP, SKSSKS, SS , etc. to converge individually at antipodal distances after being diffracted, reflected or refracted at discontinuities. This focusing strongly amplifies each signal up to almost one order of magnitude with respect to the normal phase recorded two or more degrees away. Since the signal/noise ratio is enhanced in the same proportion, seismograms at antipodal distances provide clear and strong arrivals of otherwise weak phases. Antipodal monitoring of seismic waves is suggested as a powerful means of exploring the Earth's interior. The study of these 'seismic images' generated at focal points of seismic rays will yield information on the departures from lateral homogeneity and sphericity of the core, as well as stronger constraints on earth models. To interpret the observations correctly, the data must be compared with theoretically generated seismograms. Since the appropriate ray theory equations (see, e.g. Scholte; Gilbert & Helmberger; Richards) are singular at Δ=180°, a corrective measure is taken which provides a formal expression for the wave amplitude that remains finite at the antipode, and reproduces the usual expressions at other distances.     

A CO-ORDINATE SYSTEM FOR STUDYING INTERACTIONS IN THE PRIMARY CHRISTALLER LATTICE∗

The co-ordinate system (x, y) for the triangular Christaller lattice is generalized by the addition of a third, dependent, z-axis. The extended system yields the lattice distances between lattice points, whereas the original system yields only the plane Euclidean distance.     

Urban parks as shared spaces? The utility of alert distances as indicators of avian tolerance of humans in Stirling, Scotland

Urban avian foraging is strongly affected by approaching people. Avian alert distances, the instant of a bird's appraisal of human intrusion, have not been studied in a comparative mode for passerines, despite their prominent ecological importance in parks. Alert distances for 13 passerines were examined in parks in Stirling, Scotland, using an innovative approach emphasizing human behaviour and periods between alert and flight distances, termed alert periods. Larger species were less tolerant of humans, although attracted to human wastes. Alert distances also varied according to vegetation variation. Park design may use alert distances to plan vegetation layout as well as reduce disturbing human behaviour.     

区域城镇空间格局的识别方法及案例分析

通过分析城镇之间的空间关系,探讨了区域城镇空间格局的定量化识别方法。该方法包含3个步骤：一是通过人口、产业或交通优势度的分析,识别具有较大发展潜力的城市、城镇或城镇集聚区（空间节点）。二是以空间节点之间的交通联系及其未来发展变化情况为依据,利用多维尺度分析方法展现城镇之间的空间关系（空间联系）。三是确定城镇空间影响范围,进而确定城镇空间体系的整体架构（空间圈域）。以广西西江流域7个地级市为例,运用该方法,分析了2000年以来广西西江黄金水道及区域性综合交通体系的建设对区域城镇体系产生的影响,对未来城镇空间格局的变化进行了预测。     

Diversity of terrestrial avifauna in response to distance from the shoreline of the Salton Sea

Large aquatic bodies influence surrounding terrestrial ecosystems by providing water and nutrients. In arid landscapes, the increased primary productivity that results may greatly enhance vertebrate biodiversity. The Salton Sea, a large saline lake in the Colorado Desert of southern California, provides nutrients in the form of hundreds of thousands of dead fish carcasses, brine flies, and chemical compounds through windborne salt sea spray. We performed point counts for landbirds and shorebirds monthly or every other month between March 2001 and February 2002 across a sampling grid of 35 points along the west edge of Salton Sea. We found that avian diversity (numbers of species and numbers per species) was dependent on proximity to the Sea. Diversity was at a maximum nearest the shore, and was significantly lower away from the Sea's edge, at all surveyed distances up to 1 km from the shore. Cover by the dominant shrubs on the study site also corresponded to proximity to the water's edge. Whereas one may hypothesize that the avian diversity patterns are caused by these differences in vegetation structure, our data did not support this. Future studies should further investigate this potential correlation between vegetation and bird patterns. Until more is understood about the relationship between elevated avian diversity and the physical environment of the land-shore interface, our results suggest that the Sea's surface be stabilized near its present level. Future management schemes at the Salton Sea that include reductions of water sources should be carefully analyzed, so as to not jeopardize the terrestrial avifauna at this unique ecosystem.     

缓冲区生成的边界追踪算法优化技术

利用缓冲区边界曲线上各点距缓冲目标距离相等的性质,建立一种基于矢量追踪思想的缓冲区生成方法.提出并探讨了以下优化技术:进行缓冲目标弧段重采样;扩展弧段数据结构以提高点、弧距离计算的效率;闭合边界追踪过程中采用折半逼近的追踪策略并进行动态数据压缩;对缓冲目标集合进行自适应分组和运用分治算法等.结果表明.该算法在内存占用、计算精度等方面具有优势,其计算效率亦可满足一般的GIS应用需求;此外,该算法中边界追踪的思想可以推广应用于空间分析算法设计中.     

Lacustrine basin hydrocarbon exploration – current thoughts

Although much of the world's petroleum resource-base is associated with marine systems, regionally lacustrine petroleum systems are important. Individual accumulations may exceed several billion barrels. In each of these cases the oil is derived from a lacustrine source rock and may be produced from either nonmarine or marine reservoir rocks. The purpose of this paper is to describe the factors that control lacustrine source rock development and the nature of lacustrine reservoirs. Lacustrine oils display different physical and chemical characteristics than their marine counterparts. These differences can be related to the nature of their precursor material. Although the nature of the products are different, the geochemical threshold criteria for defining source rocks in both settings are the same because of common expulsion requirements. Commercially significant lacustrine systems require the presence of large, long-lived lakes. Such lake settings are tectonic in origin and restricted to climatic settings where precipitation exceeds evaporation. Within these large lake systems three primary factors determine source rock potential and quality. These factors are primary productivity level, organic preservation potential, and matrix sedimentation rate, which controls the dilution of preserved organic matter. Source rock potential is maximized where both productivity and preservation potential are maximized and sedimentation rate is minimized. To some degree these factors can compensate for each other. Hydrocarbon reservoir potential within lacustrine basins is partially impacted by overall tectonic setting. Within extensional settings, transport distances tend to be limited, with much of the sediment being transported away from the basin. The sediments delivered to the lake are poorly sorted and sedimentologically immature, commonly resulting in poor reservoirs due to both primary properties and their susceptibility to diagenesis. Within rifts better reservoirs tend to develop along platform or flexural margins. Stacking of reservoirs is important in lacustrine systems but baffles and barriers are often present between individual sand units. These barriers form as a result of lake level fluctuations. In compressional settings transport distances tend to be longer, resulting in more mature, better sorted sediments leading to higher quality reservoirs. These reservoirs typically develop in fluvial-deltaic and wave-dominated shoreline settings. Lacustrine carbonate reservoirs are locally important. These carbonates tend to develop during lake level lowstands and are dependent on diagenesis (dissolution and karstification) for porosity and permeability development. Lacustrine reservoirs are often stratigraphically and areally limited and display low individual well production rates. Within pure lacustrine systems exploration opportunities appear to be often restricted by either reservoir presence or quality (i.e., production rates). The best exploration opportunities in lacustrine basins appear to be associated with hybrid systems where a lacustrine source and marine reservoir exist.     

DEM格网与畸变遥感影像的一体化显示研究

遥感影像可以极大地增强DEM的表达效果,然而由于各种因素的影响,通常需对其进行预处理,传统方法是通过同名控制点进行校正。该文提出一种新的自动匹配算法,即提取DEM和遥感影像对应的特征线,利用Douglas-Peucker算法提取对应的特征点,以DEM特征点为离散点进行Delaunay三角剖分,并基于TIN完成纹理映射。实验结果表明,该算法显示效果较好,可有效改善畸变图像引起的错误显示。