| 1. |
- Brandt, S. Anders, 1970-
(författare)
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Modeling and visualizing uncertainties of flood boundary delineation : algorithm for slope and DEM resolution dependencies of 1D hydraulic models
- 2016
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Ingår i: Stochastic environmental research and risk assessment (Print). - : Springer. - 1436-3240 .- 1436-3259. ; 30:6, s. 1677-1690
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Tidskriftsartikel (refereegranskat)abstract
- As flood inundation risk maps have become a central piece of information for both urban and risk management planning, also a need to assess the accuracies and uncertainties of these maps has emerged. Most maps show the inundation boundaries as crisp lines on visually appealing maps, whereby many planners and decision makers, among others, automatically believe the boundaries are both accurate and reliable. However, as this study shows, probably all such maps, even those that are based on high-resolution digital elevation models (DEMs), have immanent uncertainties which can be directly related to both DEM resolution and the steepness of terrain slopes perpendicular to the river flow direction. Based on a number of degenerated DEMs, covering areas along the Eskilstuna River, Sweden, these uncertainties have been quantified into an empirically-derived disparity distance equation, yielding values of distance between true and modeled inundation boundary location. Using the inundation polygon, the DEM, a value representing the DEM resolution, and the desired level of confidence as inputs in a new-developed algorithm that utilizes the disparity distance equation, the slope and DEM dependent uncertainties can be directly visualized on a map. The implications of this strategy should benefit planning and help reduce high costs of floods where infrastructure, etc., have been placed in flood-prone areas without enough consideration of map uncertainties.
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| 2. |
- Brandt, S. Anders, 1970-, et al.
(författare)
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Visualising DEM-related flood-map uncertainties using a disparity-distance equation algorithm
- 2016
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Ingår i: IAHS-AISH Proceedings and Reports. - Göttingen : Copernicus Publications on behalf of International Association of Hydrological Sciences (IAHS). ; , s. 153-159
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Konferensbidrag (refereegranskat)abstract
- The apparent absoluteness of information presented by crisp-delineated flood boundaries can lead tomisconceptions among planners about the inherent uncertainties associated in generated flood maps. Even mapsbased on hydraulic modelling using the highest-resolution digital elevation models (DEMs), and calibrated withthe most optimal Manning’s roughness (n) coefficients, are susceptible to errors when compared to actual floodboundaries, specifically in flat areas. Therefore, the inaccuracies in inundation extents, brought about by thecharacteristics of the slope perpendicular to the flow direction of the river, have to be accounted for. Instead ofusing the typical Monte Carlo simulation and probabilistic methods for uncertainty quantification, an empiricalbaseddisparity-distance equation that considers the effects of both the DEM resolution and slope was used tocreate prediction-uncertainty zones around the resulting inundation extents of a one-dimensional (1-D) hydraulicmodel. The equation was originally derived for the Eskilstuna River where flood maps, based on DEM dataof different resolutions, were evaluated for the slope-disparity relationship. To assess whether the equation isapplicable to another river with different characteristics, modelled inundation extents from the Testebo Riverwere utilised and tested with the equation. By using the cross-sectional locations, water surface elevations, andDEM, uncertainty zones around the original inundation boundary line can be produced for different confidences.The results show that (1) the proposed method is useful both for estimating and directly visualising modelinaccuracies caused by the combined effects of slope and DEM resolution, and (2) the DEM-related uncertaintiesalone do not account for the total inaccuracy of the derived flood map. Decision-makers can apply it to alreadyexisting flood maps, thereby recapitulating and re-analysing the inundation boundaries and the areas that areuncertain. Hence, more comprehensive flood information can be provided when determining locations whereextra precautions are needed. Yet, when applied, users must also be aware that there are other factors that caninfluence the extent of the delineated flood boundary.
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| 3. |
- Jiang, Bin, 1965-, et al.
(författare)
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A Fractal Perspective on Scale in Geography
- 2016
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Ingår i: ISPRS International Journal of Geo-information. - : MDPI AG. - 2220-9964. ; 5:6
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Tidskriftsartikel (refereegranskat)abstract
- Scale is a fundamental concept that has attracted persistent attention in geography literature over the past several decades. However, it creates enormous confusion and frustration, particularly in the context of geographic information science, because of scale-related issues such as image resolution and the modifiable areal unit problem (MAUP). This paper argues that the confusion and frustration arise from traditional Euclidean geometric thinking, in which locations, directions, and sizes are considered absolute, and it is now time to revise this conventional thinking. Hence, we review fractal geometry, together with its underlying way of thinking, and compare it to Euclidean geometry. Under the paradigm of Euclidean geometry, everything is measurable, no matter how big or small. However, most geographic features, due to their fractal nature, are essentially unmeasurable or their sizes depend on scale. For example, the length of a coastline, the area of a lake, and the slope of a topographic surface are all scale-dependent. Seen from the perspective of fractal geometry, many scale issues, such as the MAUP, are inevitable. They appear unsolvable, but can be dealt with. To effectively deal with scale-related issues, we present topological and scaling analyses illustrated by street-related concepts such as natural streets, street blocks, and natural cities. We further contend that one of the two spatial properties, spatial heterogeneity, is de facto the fractal nature of geographic features, and it should be considered the first effect among the two, because it is global and universal across all scales, which should receive more attention from practitioners of geography.
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| 4. |
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| 5. |
- Lim, Nancy Joy, 1980-, et al.
(författare)
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Are Feature Agreement Statistics Alone Sufficient to Validate Modelled Flood Extent Quality? : A Study on Three Swedish Rivers Using Different Digital Elevation Model Resolutions
- 2019
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Ingår i: Mathematical problems in engineering (Print). - : Hindawi Publishing Corporation. - 1024-123X .- 1563-5147. ; 2019
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Tidskriftsartikel (refereegranskat)abstract
- Hydraulic modelling is now, at increasing rates, used all over the world to provide flood risk maps for spatial planning, flood insurance, etc. This puts heavy pressure on the modellers and analysts to not only produce the maps but also information on the accuracy and uncertainty of these maps. A common means to deliver this is through performance measures or feature statistics. These look at the global agreement between the modelled flood area and the reference flood that is used. Previous studies have shown that the feature agreement statistics do not differ much between models that have been based on digital elevation models (DEMs) of different resolutions, which is somewhat surprising since most researchers agree that high-resolution DEMs are to be preferred over poor resolution DEMs. Hence, the aim of this study was to look into how and under which conditions the different feature agreement statistics differ, in order to see when the full potential of high-resolution DEMs can be utilised. The results show that although poor resolution DEMs might produce high feature agreement scores (around F > 0.80), they may fail to provide good flood extent estimations locally, particularly when the terrain is flat. Therefore, when high-resolution DEMs (1 to 5 m) are used, it is important to carefully calibrate the models by the use of the roughness parameter. Furthermore, to get better estimates on the accuracy of the models, other performance measures such as distance disparities should be considered.
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| 6. |
- Lim, Nancy Joy, 1980-, et al.
(författare)
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Flood map boundary sensitivity due to combined effects of DEM resolution and roughness in relation to model performance
- 2019
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Ingår i: Geomatics, Natural Hazards and Risk. - : Taylor & Francis. - 1947-5705 .- 1947-5713. ; 10:1, s. 1613-1647
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Tidskriftsartikel (refereegranskat)abstract
- In comprehending flood model results, we performed sensitivity analyses and evaluated how different combinations of digital elevation model (DEM) resolution and Manning’s roughness affect flood maps produced from a 2D hydraulic model. Moreover, we analysed how the estimation of accuracy can further be influenced by the performance measure and the area’s topography. Various combinations of DEM and Manning’s n produced different results, in terms of quantified performance in relation to actual flood extent and the generated flood boundaries. High-resolution DEMs performed better with higher Manning’s n, while lower n values were better for lower resolution DEMs. Furthermore, although lower resolution DEMs (25 and 50 m) received higher quantified performances, there are more discrepancies in the flood maps and water surface elevations (WSE) produced by them. The current statistical estimators of model performance do not necessarily provide an accurate estimate of which combination of DEM resolution and roughness are more suitable for application to modelling. Different statistical estimates have different assumptions, which can affect the model selection. Therefore, a more holistic approach towards model selection should be adopted that gives equal importance to statistical estimators, as well as the quality of flood inundation extents.
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| 7. |
- Lim, Nancy Joy, 1980-
(författare)
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Modelling, mapping and visualisation of flood inundation uncertainties
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Flood maps showing extents of predicted flooding for a given extreme event have wide usage in all types of spatial planning tasks, as well as serving as information material for the public. However, the production processes that these maps undergo (including the different data, methods, models and decisions from the persons generating them), which include both Geographic Information Systems (GIS) and hydraulic modelling, affect the map’s content, and will be reflected in the final map. A crisp flood boundary, which is a common way of representing the boundary in flood maps, may therefore not be the best representation to be used. They provide a false implication that these maps are correct and that the flood extents are absolute, despite the effects of the entire modelling in the prediction output. Hence, this research attempts to determine how flood prediction outputs can be affected by uncertainties in the modelling process. In addition, it tries to evaluate how users understand, utilise and perceive flood uncertainty information. Three main methods were employed in the entire research: uncertainty modelling and analyses; map and geovisualisation development; and user assessment. The studies in this work showed that flood extents produced were influenced by the Digital Elevation Model (DEM) resolution and the Manning’s used. This effect was further increased by the topographic characteristic of the floodplain. However, the performance measure used, which quantify how well a model produces result in relation to a reference floor boundary, had also biases in quantifying outputs. Determining the optimal model output, therefore, depended on outcomes of the goodness-of-fit measures used. In this research, several ways were suggested on how uncertainties can be visualised based on the data derived from the uncertainty assessment and by characterising the uncertainty information. These can be through: dual-ended maps; flood probability maps; sequential maps either highlighting the degrees of certainty (certainty map) or degrees of uncertainty (uncertainty map) in the data; binary maps; overlain flood boundaries from different calibration results; and performance bars. Different mapping techniques and visual variables were used for their representation. These mapping techniques employed, as well as the design of graphical representation, helped facilitate understanding the information by the users, especially when tested during the evaluations. Note though that there were visualisations, which the user found easier to comprehend depending on the task given. Each of these visualisations had also its advantages and disadvantages in communicating flood uncertainty information, as shown in the assessments conducted. Another important aspect that came out in the study was how the users’ background influence decision-making when using these maps. Users’ willingness to take risks depended not only on the map, but their perceptions on the risk itself. However, overall, users found the uncertainty maps to be useful to be incorporated in planning tasks.
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| 8. |
- Lim, Nancy Joy, 1980-, et al.
(författare)
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Visualisation and evaluation of flood uncertainties based on ensemble modelling
- 2016
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Ingår i: International Journal of Geographical Information Science. - : Taylor & Francis. - 1365-8816 .- 1365-8824 .- 1362-3087. ; 30:2, s. 240-262
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Tidskriftsartikel (refereegranskat)abstract
- This study evaluates how users incorporate visualisation of flood uncertainty information in decision-making. An experiment was conducted where participants were given the task to decide building locations, taking into account homeowners’ preferences as well as dilemmas imposed by flood risks at the site. Two general types of visualisations for presenting uncertainties from ensemble modelling were evaluated: (1) uncertainty maps, which used aggregated ensemble results; and (2) performance bars showing all individual simulation outputs from the ensemble. Both were supplemented with either two-dimensional (2D) or three-dimensional (3D) contextual information, to give an overview of the area.The results showed that the type of uncertainty visualisation was highly influential on users’ decisions, whereas the representation of the contextual information (2D or 3D) was not. Visualisation with performance bars was more intuitive and effective for the task performed than the uncertainty map. It clearly affected users’ decisions in avoiding certain-to-be-flooded areas. Patterns to which the distances were decided from the homeowners’ preferred positions and the uncertainties were similar, when the 2D and 3D map models were used side by side with the uncertainty map. On the other hand, contextual information affected the time to solve the task. With the 3D map, it took the participants longer time to decide the locations, compared with the other combinations using the 2D model.Designing the visualisation so as to provide more detailed information made respondents avoid dangerous decisions. This has also led to less variation in their overall responses.
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| 9. |
- Milutinovic, Goran, et al.
(författare)
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The impact of interactive visualization on trade-off-based geospatial decision-making
- 2019
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Ingår i: International Journal of Geographical Information Science. - : Taylor & Francis. - 1365-8816 .- 1365-8824 .- 1362-3087. ; 33:10, s. 2094-2123
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Tidskriftsartikel (refereegranskat)abstract
- In a previous work we developed GISwaps, a novel method for geospatial decision-making based on Even Swaps. In this paper, we present the results of an evaluation of a visualization framework integrated with this method, implemented within a decision support system. This evaluation is based on two different studies. In the quantitative study, 15 student participants used GISwaps with no visual features, and 15 participants used GISwaps with the integrated visual framework, as the tool in a solar farm site location case study. The results of the quantitative evaluation show positive impact of the visualization in terms of increased coherency in trade-offs. The results also show a statistically significant difference in average trade-off values between the groups, with users from the non-visual group setting on average 20% higher trade-off values compared with the users in the visual group. In the qualitative study, we had one expert in GIS, two experts in decision-making and two experts in solar energy as a focus user group. Data in this study were obtained by observations and semi-structured interviews with the participants. The impact of the visualization framework was assessed positively by all participants in the expert group.
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| 10. |
- Myagmartseren, Purevtseren, 1975-, et al.
(författare)
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Implications of a Spatial Multicriteria Decision Analysis for Urban Development in Ulaanbaatar, Mongolia
- 2017
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Ingår i: Mathematical problems in engineering (Print). - : Hindawi Publishing Corporation. - 1024-123X .- 1563-5147. ; 2017
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Tidskriftsartikel (refereegranskat)abstract
- New technology has provided new tools for effective spatial planning. Through the example of locating suitable sites for urbandevelopment in Ulaanbaatar, this paper illustrates how multicriteria decision analysis and geographical information systems canbe used for more effective urban planning. Several constraint and factor criteria were identified, transformed into map layers,and weighted together using the analytic hierarchy process. Besides localization results, this study shows the effect of using poorelevation data and how a sensitivity analysis can be applied to yield further information, spot weighting weaknesses, and assess thequality of the criteria.
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