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1.
WebGIS (also known as web‐based GIS and Internet GIS) denotes a type of Geographic Information System (GIS), whose client is implemented in a Web browser. WebGISs have been developed and used extensively in real‐world applications. However, when such a complex web‐based system involves the dissemination of large volumes of data and/or massive user interactions, its performance can become an issue. In this paper, we first identify several major potential performance problems with WebGIS. Then, we discuss several possible techniques to improve the performance. These techniques include the use of pyramids and hash indices on the server side to handle large images. To resolve server‐side conflicts originating from concurrent massive access and user interactions, we suggest clustering and multithreading techniques. Multithreading is also used to break down the long sequential, layer‐based data access to concurrent data access on the client side. Caching is suggested as a means to enhance concurrent data access for the same datasets on both the server and the client sides. The technique of client‐side dynamic data requests is used to improve data transmission. Compressed binary representation is implemented on both sides to reduce transmission volume. We also compare the performance of a prototype WebGIS with and without these techniques.  相似文献   

2.
Many parts of the world with young mountain chains, such as the Himalayas, are highly susceptible to landslides. Due to general ruggedness and steep slopes, roads provide the only way of transportation and connectivity in such terrains. Generally, landslide hazards are overlooked during route planning. In this study, in a test area in the Himalayas, various thematic layers, viz. landslide distribution, landslide hazard zonation, landuse/landcover, drainage order and lithology are generated and integrated using Remote Sensing–GIS techniques. The integrated data layer in raster form has been called a ‘thematic cost map’ and provides an estimate of the cost of route development and maintenance. The relative cost assignment is based on experts' knowledge. Route planning is based on neighbourhood analysis to find various movement possibilities from a pixel to its immediate neighbours. A number of patterns such as those analogous to movements in chess games have been considered. Two new neighbourhood patterns, named here Knight31 and Knight32, have been conceived in addition to commonly used Rook, Bishop and Knight patterns. The neighbourhood movement cost for moving from one pixel to a connected neighbour has been calculated for a 7×7 pixel window considering distance, gradient cost and thematic cost. Dijkstra's algorithm has been applied to compute the least‐cost route between source and destination points. A few examples are presented to show the utility of this approach for a landslide‐safe automatic route planning for a highly rugged hilly terrain.  相似文献   

3.
Most multiple‐flow‐direction algorithms (MFDs) use a flow‐partition coefficient (exponent) to determine the fractions draining to all downslope neighbours. The commonly used MFD often employs a fixed exponent over an entire watershed. The fixed coefficient strategy cannot effectively model the impact of local terrain conditions on the dispersion of local flow. This paper addresses this problem based on the idea that dispersion of local flow varies over space due to the spatial variation of local terrain conditions. Thus, the flow‐partition exponent of an MFD should also vary over space. We present an adaptive approach for determining the flow‐partition exponent based on local topographic attribute which controls local flow partitioning. In our approach, the influence of local terrain on flow partition is modelled by a flow‐partition function which is based on local maximum downslope gradient (we refer to this approach as MFD based on maximum downslope gradient, MFD‐md for short). With this new approach, a steep terrain which induces a convergent flow condition can be modelled using a large value for the flow‐partition exponent. Similarly, a gentle terrain can be modelled using a small value for the flow‐partition exponent. MFD‐md is quantitatively evaluated using four types of mathematical surfaces and their theoretical ‘true’ value of Specific Catchment Area (SCA). The Root Mean Square Error (RMSE) shows that the error of SCA computed by MFD‐md is lower than that of SCA computed by the widely used SFD and MFD algorithms. Application of the new approach using a real DEM of a watershed in Northeast China shows that the flow accumulation computed by MFD‐md is better adapted to terrain conditions based on visual judgement.  相似文献   

4.
Mine contamination is one of the main obstacles to economic recovery and other types of progress in mine‐affected countries. Therefore, the primary goal of humanitarian demining operations is to clear all suspected minefields and restore them so as to make them available for their previous use. The customary financial shortfall results in the need for priority setting in the mine removal process. This paper describes and investigates a new approach to priority setting within mine action, with the introduction of a hierarchic GIS‐based decision support system (DSS). The proposed DSS is aimed at determining the objective priorities required to reduce the risks stemming from mine contamination. DSS is based on a combination of GIS analysis and a multicriteria method in order to enable efficacious mine action management, namely setting humanitarian demining priorities in order to optimally reduce the risk caused by mines. GIS is outlined as a powerful tool for the generation of aggregated information used in multicriteria analysis, as is the link between hierarchic decision levels in the proposed DSS. The results of a demonstration of the proposed GIS‐based DSS on mine‐affected water resources in Croatia are supplied.  相似文献   

5.
Several application domains require handling spatio‐temporal data. However, traditional Geographic Information Systems (GIS) and database models do not adequately support temporal aspects of spatial data. A crucial issue relates to the choice of the appropriate granularity. Unfortunately, while a formalisation of the concept of temporal granularity has been proposed and widely adopted, no consensus exists on the notion of spatial granularity. In this paper, we address these open problems, by proposing a formal definition of spatial granularity and by designing a spatio‐temporal framework for the management of spatial and temporal information at different granularities. We present a spatio‐temporal extension of the ODMG type system with specific types for defining multigranular spatio‐temporal properties. Granularity conversion functions are introduced to obtain attributes values at different spatial and temporal granularities.  相似文献   

6.
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7.
Det er ikke så mange steder i vårt land vindens virkninger på jordoverflaten er så stor at man legger særlig merke til den. Nedbøren er de fleste steder så stor og plantedekket så tett at selv den letteste og fineste sand bindes så godt at vinden ikke får tak.

De fleste steder der flyvesandfelter finnes er det strandsanden som leverer materlalet. Fra stranden blåser vinden sanden op i hauger og rygger, de såkalte dyner, og det fineste materiale spredes som støv i luften og føres lengere bort. Våre største flyvesandfelter ligger på Jæren. Her har sandflukten gjort ikke liten skade og man søker å dempe den ved plantning av strandrug og marehalm. I sin avhandling: »Hvordan Norges jord blev til« nevner dr. G. Holmsen dynesandfelter pa Lista, Sunnmore og Andoy, og »flere steder i Finnnmark«. Selv har jeg sett flyvesandfelter ved dampskibsleden pa Fugløy og i Gildeskål i Nordland.  相似文献   

8.
Conventional methods have difficulties in forming optimal paths when raster data are used and multi‐objectives are involved. This paper presents a new method of using ant colony optimization (ACO) for solving optimal path‐covering problems on unstructured raster surfaces. The novelty of this proposed ACO includes the incorporation of a couple of distinct features which are not present in classical ACO. A new component, the direction function, is used to represent the ‘visibility’ in the path exploration. This function is to guide an ant walking toward the final destination more efficiently. Moreover, a utility function is proposed to reflect the multi‐objectives in planning applications. Experiments have shown that classical ACO cannot be used to solve this type of path optimization problems. The proposed ACO model can generate near optimal solutions by using hypothetical data in which the optimal solutions are known. This model can also find the near optimal solutions for the real data set with a good convergence rate. It can yield much higher utility values compared with other common conventional models.  相似文献   

9.
We use a GIS‐based agent‐based model (ABM), named dynamic ecological exurban development (DEED), with spatial data in hypothetical scenarios to evaluate the individual and interacting effects of lot‐size zoning and municipal land‐acquisition strategies on possible forest‐cover outcomes in Scio Township, a municipality in Southeastern Michigan. Agent types, characteristics, behavioural methods, and landscape perceptions (i.e. landscape aesthetics) are empirically informed using survey data, spatial analyses, and a USDA methodology for mapping landscape aesthetic quality. Results from our scenario experiments computationally verified literature that show large lot‐size zoning policies lead to greater sprawl, and large lot‐size zoning policies can lead to increased forest cover, although we found this effect to be small relative to municipal land acquisition. The return on land acquisition for forest conservation was strongly affected by the location strategy used to select parcels for conservation. Furthermore, the location strategy for forest conservation land acquisition was more effective at increasing aggregate forest levels than the independent zoning policies, the quantity of area acquired for forest conservation, and any combination of the two. The results using an integrated GIS and ABM framework for evaluating land‐use development policies on forest cover provide additional insight into how these types of policies may act out over time and what aspects of the policies were more influential towards the goal of maximising forest cover.  相似文献   

10.
Historical GIS has the potential to re‐invigorate our use of statistics from historical censuses and related sources. In particular, areal interpolation can be used to create long‐run time‐series of spatially detailed data that will enable us to enhance significantly our understanding of geographical change over periods of a century or more. The difficulty with areal interpolation, however, is that the data that it generates are estimates which will inevitably contain some error. This paper describes a technique that allows the automated identification of possible errors at the level of the individual data values.  相似文献   

11.
Empirical models designed to simulate and predict urban land‐use change in real situations are generally based on the utilization of statistical techniques to compute the land‐use change probabilities. In contrast to these methods, artificial neural networks arise as an alternative to assess such probabilities by means of non‐parametric approaches. This work introduces a simulation experiment on intra‐urban land‐use change in which a supervised back‐propagation neural network has been employed in the parameterization of several biophysical and infrastructure variables considered in the simulation model. The spatial land‐use transition probabilities estimated thereof feed a cellular automaton (CA) simulation model, based on stochastic transition rules. The model has been tested in a medium‐sized town in the Midwest of São Paulo State, Piracicaba. A series of simulation outputs for the case study town in the period 1985–1999 were generated, and statistical validation tests were then conducted for the best results, based on fuzzy similarity measures.  相似文献   

12.
This paper presents a fuzzy inference guided cellular automata approach. Semantic or linguistic knowledge on urban development is expressed as fuzzy rules, based on which fuzzy inference is applied to determine the urban development potential for each pixel. A defuzzification process converts the development potential to the required neighbourhood development level, which is taken by cellular automata as initial approximation for its transition rules. Such approximations are updated through spatial calibration over townships and temporal calibration with multi‐temporal satellite images. Assessment of the modelling results is based on three evaluation measures: fitness and Type I and Type II errors. The approach is applied to model the growth of the city of Indianapolis, Indiana over a period of 30 years from 1973 to 2003. A fitness level of 100 ±20% with 30% average errors can be achieved for 80% of the townships in urban‐growth prediction.  相似文献   

13.
Ethical dilemmas involving issues of harm-benefit, privacy, deception, and sponsor relations are encountered frequently in geographical research. Geographers have not always been sensitive to ethical issues, nor have they always been able to reconcile their obligations to understanding and knowledge with those of respecting the dignity and integrity of research subjects. This paper reviews these fundamental ethical concerns. Four strategies for handling ethical difficulties are reviewed: individual self-regulation, disciplinary responses, institutional controls, and external controls. Individual self-regulation is recommended.  相似文献   

14.
A new raster‐based GIS model that combines multi‐criteria evaluation and least‐cost path analysis was developed to determine the optimal haulage routes of dump trucks in large scale open‐pit mines. The model logic can consider multiple criteria simultaneously (i.e. speed, water body, ore body, curve, visibility, haul road maintenance) and can rate the adverse factor scores of truck movement using fuzzy membership functions. After establishing the weights of five factors by pairwise comparisons, the average adverse score grid can be generated by the weighted linear combination of factor and constraint scores. New software, called Dump Traveler, was implemented to improve the availability of the developed model. An application to the Roto South pit in the Pasir open‐pit coal mine, Indonesia, showed that the software can provide rational solutions to determine the optimal routes on truck haulage operations. Moreover, the layout of available haul roads can be evaluated to consider the trade‐off between road maintenance costs and the potential for traffic jams. Variations of weights for factors were found to be sensitive to the optimal haulage routes determined by least‐cost path analysis. The software provides both optimal routes on truck haulage operations and approximately estimated travel times along the routes, therefore it can support other truck dispatching software that mainly considers scheduling problems.  相似文献   

15.
Kirkup et al. (1998) [Australian Geographer 29, pp. 241–55] criticise our theory of alternating flood regimes and question its application to river management. A brief but critical appraisal of their work shows many errors and misrepresentations. When these are corrected, their challenge is found deficient.  相似文献   

16.
While current Geographic Information Systems (GISs) can represent observational spatial data well, they have limited capabilities in representing some non‐observational social elements and goal‐driven behaviours that can be important factors in a wide range of geographic issues. Such social components may include laws, regulations, polices, plans, culture, and customs, as well as their relations and interactions with the geographic environment at different scales. Getting beyond traditional data‐centred approaches, this research presents a knowledge‐oriented strategy in order to address these issues within a GIS context. We incorporate two major conceptual elements. First, extending from conventional agent notions and their geographic applications, geographic agents (GeoAgents) are considered as a basic representation component to specifically address social rules and goal‐driven behaviours that impact the Earth and environmental systems. Second, in order to incorporate GeoAgents with current space–time representation, a new conceptual representation framework, called ‘fields, objects, time, GeoAgents, and relations’ (FOTAR), is introduced to address the cross‐scale processes of both social and natural interactions. A Java‐based prototype, GeoAgent‐based Knowledge System (GeoAgentKS), is described to implement this framework by integrating agent technologies with multiple data and knowledge representation techniques, such as expert systems, concept maps, mathematical models, and geospatial databases. The application of this prototype in a case study is also presented, investigating scale‐dependent human–environment interactions under different emergency situations for community water systems in Central Pennsylvania, USA. In this case study, a systematic set of methodologies of knowledge acquisition, representation, and confirmation for constructing GeoAgents' knowledge bases by using expert systems were explored to formalize high‐level knowledge and social behaviours in the FOTAR‐based representations. The results show that the proposed conceptual representation framework is achievable at both implementation and application levels, and the prototype tool is demonstrated to be valuable in facilitating knowledge sharing, policymaking, municipal management, and decision‐making, especially for real‐world emergency management.  相似文献   

17.
This paper discusses extensions of GAP‐trees from three aspects and its implementation based on non‐topological structure in order to enhance access to large vector data sets. First of all, we apply cartographic generalization rules to build a generalization procedure of the GAP‐tree, which makes coarse representations more consistent with human cognition. Second, we replace the three‐dimensional (pseudo‐) Reactive‐tree index with a 2D R‐tree index and a B‐tree index to improve the system efficiency. Finally, we compress a binary GAP‐tree into multi‐way GAP‐trees in order to reduce data redundancy. The shallower multi‐way GAP‐trees not only eliminate redundant data but also accelerate the system's response time. The extensions have been successfully implemented in PostgreSQL. A test of Beijing's land‐use data at the 1:10 000 scale demonstrates that the extended GAP‐trees are efficient, compact, and easy to implement.  相似文献   

18.
Hypolimnetic oxygen depletion has been accelerated in many lakes due to cultural eutrophication. However, the extent and magnitude of environmental change is difficult to ascertain due to the lack of historical records. Larval Chironomidae (Diptera) are useful proxy indicators of oxygen, as they show a wide range of tolerances to oxygen conditions and their chitinous head capsules preserve well in lake sediments. Using paleolimnological techniques, chironomid assemblages from the surface sediments of 42 southeastern Ontario lakes were related to environmental conditions. Hypolimnetic oxygen conditions, measured as the average endofsummer hypolimnetic dissolved oxygen (AvgDO(Summ)), explained the most variation in the chironomid assemblages, whereas dissolved inorganic carbon, the Anoxic Factor, max. depth and total phosphorus concentrations were also correlated with assemblage composition. Based on the relative abundances of 45 chironomid taxa, a robust, partial least squares (PLS) regression transfer function for AvgDO(Summ) was constructed (r2 = 0.74, r2 (jack) = 0.58, n = 40). This new transfer function should allow paleolimnologists to directly track past trends in hypolimnetic oxygen levels.  相似文献   

19.
Hazard interactions in glacial and periglacial environments are of crucial importance due to their potential for causing major catastrophes. Nevertheless, glacial and periglacial hazards have usually been modeled separately to date. In this study, we therefore propose a methodological strategy for modeling and assessing glacial and periglacial hazard interactions on a regional scale, including ice avalanches, lake outbursts and periglacial debris flows. Due to climate‐related rapid changes in glacial and periglacial areas, methods which incorporate monitoring capacities are needed. Hence, the methods presented here are based on remote sensing data, which are particularly powerful for monitoring tasks, and GIS modeling. For ice avalanche and lake‐outburst hazard detection and modeling, we applied recently published methods based on Landsat‐TM imagery, terrain modeling and flow routing. For detection of potential debris‐flow initiation zones in steep debris reservoirs, we present a novel method based on image processing of IKONOS data and terrain modeling, followed by flow modeling. Using this method, we achieve the synthesis of the individual process modeling in order to assess the potential interactions. The modeling is applied to a study region in the central Swiss Alps. The results show that systematic modeling based on remote sensing and GIS is suitable for first‐order assessment of glacial and periglacial hazard interactions as well as assessments of possible consequences, including impacts on traffic routes and other infrastructure. Based on this, critical cases can be detected and analyzed by subsequent detailed studies.  相似文献   

20.
Visibility computation on terrain models is an important research topic with many applications in Geographical Information Systems. A multi‐visibility map is the subdivision of the domain of a terrain into regions that, according to different criteria, encodes the visibility with respect to a set of view elements. We present an approach for visualising approximated multi‐visibility maps of a triangulated terrain corresponding to a set of view elements by using graphics hardware. Our method supports heterogeneous sets of view elements containing points, segments, polygonal chains and polygons and works for weak and strong visibility. Moreover, we are also able to efficiently solve approximated point and polygonal region multi‐visibility queries. To illustrate the usefulness of our approach we present results obtained with an implementation of the proposed algorithms.  相似文献   

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