Automated placement of supplementary contour lines

Supplementary contour lines are placed between regular contour lines to visualize small but important forms that regular contour lines are unable to show. On topographic maps, typical forms are hillcrests, depressions, saddles, terraces, banks, and levees. No automated method for the selection of supplementary contour lines has been described so far. We document cartographic design principles for the selection of supplementary contour lines for topographic maps, and present an automated method for their placement. Results of the automated method are similar to manually placed supplementary contour lines. Our method helps map authors to create contour line maps that more effectively illustrate relevant small details in maps showing terrain elevation or other scalar fields.     

Accuracy of contour lines using 3D bands

This article describes a new methodology for the planimetric control of contour lines. The method is based on the generation of buffers around the contour lines which define a 3D buffer around the maximum slope line. After that we analyze the quantity of points from a more accurate source which is inside this buffer. As a result, we obtain a distribution function of the control points included when we apply several widths to the buffers. We have also determined the angularity and height differences of these points. The method has been applied to several sets of contour line intervals derived from a digital elevation model (DEM) and to the contour lines of one published topographic map using the DEM as the control source. We have also analyzed the representative behaviour of the contour lines, taking into account the contour line interval and the detection of an uncertainty model based on the slope variation. This study demonstrates the viability of the proposed method for obtaining the uncertainty of the contour lines depending on a given level of confidence and the variability of this uncertainty in the map. Finally, we propose a range of contour line intervals based on the scale and slopes.     

Improving the representation of major landforms in analytical relief shading

Relief shading is the most common type of cartographic relief representation for print and digital maps. Manual relief shading results in informative and visually pleasing representations of terrain, but it is time consuming and expensive to produce. Current analytical relief shading can be created quickly, but the resulting maps are not as aesthetically appealing and do not show landscape features in an explicit manner. This article introduces an automated digital method that produces shaded relief with locally adjusted illumination directions to simulate the techniques and cartographic principles of manual relief shading. Ridgelines and valley lines are derived from a digital terrain model, vectorized, and used in a diffusion curve algorithm. A graph analysis generalizes the lines before using them for diffusion curve shading. The direction of illumination is adjusted based on the spatial orientation of ridgelines and valley lines. The diffusion curve shading is combined with standard analytical relief shading to create a final diffusion relief shading image. Similar to manual relief shading, major landforms and the structure of the terrain are more clearly shown in the diffusion relief shading. The presented method best highlights major landforms in terrain characterized by sharp, clearly defined ridges and valleys.     

基于层次格网索引的图幅接边处等高线高程错误识别和自动修正研究

等高线蕴含的历史高程信息可有效延长地形研究的时间序列,有利于深入挖掘地形变化长期规律,然而,图幅接边处的高程属性错误降低了等高线的数据质量,制约着等高线高程信息的实际应用。针对这一问题,该文提出一种基于层次格网索引的图幅接边处等高线高程错误识别和自动修正方法:首先,将层次格网索引与方向性二邻域算法相结合,以减少数据重复计算;然后,利用等高线空间位置标签及快速排序算法构建强空间位置关系,解决图幅接边处等高线匹配的准确性问题;最后,以高程冲突位点为驱动因子进行逻辑判断,实现等高线高程错误的识别及自动修正。实验结果表明:该方法运算效率较未进行效率优化时提高了203倍,接边处等高线高程错误识别与修正精度的最大值分别达97.71%和91.40%;相较于现有方法,该方法在精度和效率方面表现更佳,对区域性错误和变形等高线具有更高的适用性。     

Utilizing the Audio-Tutorial Approach

Abstract

Construction of raised-relief maps by students in middle school to high school is a rewarding “hands-on” experience. A major feature of this project is that materials are readily available, inexpensive and manageable by students themselves. Tracing from topographic maps on to inexpensive, easily-carved materials like cardboard or foam-core board involves the student in map interpretation techniques. Concepts such as interpreting elevations from contour lines, recognizing symbolization on a map, seeing raised-relief as representing “the lay of the land,” understanding map scale, and recognition of color in representation of elevations are part of this experience. Carving and construction of the raised-relief map give the student an appreciation of topographic features in 3-D. The finished model can serve as a display and learning tool for the future.     

A Field Plan for Large-Scale Terrain Mapping

Abstract

Field work in geography often involves an exercise in which the student is required to make some type of map. Although most areas of the United States are well mapped, seldom are extremely large-scale (larger than 1:24,000) relief maps available. A method of contour-line mapping using small contour intervals and a large scale is appropriate in teaching several mapping principles and requires only a few simple tools and the use of elementary mathematics. Percent slope is established at uniform intervals along closely spaced traverses of the area to be mapped. Spot elevations are thus established from which contour lines can be determined. Accuracy in field-data collection and care in cartography will yield a very satisfactory map of terrain characteristics of small areas. Several concepts of maps and mapping are taught through direct student involvement.     

Weighted Isolines: An Alternative Method for Depicting Statistical Surfaces*

“Weighted isolines” is a method of isoline symbolization in which isolines vary in width in proportion to the data values they represent. Results of a map interpretation experiment demonstrate that the weighted isolines method is an effective alternative to conventional labeled isolines of uniform width and “shadowed” isolines (which thicken uniformly along southeastward slopes) for prompting rapid and accurate interpretation of statistical surfaces.     

Mineral-Potential Mapping for MVT Deposits with Limited Data Sets Using Landsat Data and Geological Evidence in the Borden Basin, Northern Baffin Island, Nunavut, Canada

Posterior probabilities of occurrence for Zn-Pb Mississippi Valley Type (MVT) mineralization were calculated based on evidence maps derived from regional geology, Landsat-TM, RADARSAT-1, a digital elevation model and aeromagnetic data sets in the Borden Basin of northern Baffin Island, Canada. The vector representation of geological contacts and fault traces were refined according to their characteristics identified in Landsat-TM, RADARSAT-1, DEM, slope, aspect, and shaded relief data layers. Within the study area, there is an association between the occurrence of MVT mineralization and proximity to the contact of platformal carbonates and shale units of the adjacent geological formation. A spatial association also tends to exist between mineralization and proximity to E-W and NW-SE trending faults. The relationships of known MVT occurrences with the geological features were investigated by spatial statistical techniques to generate evidence maps. Supervised classification and filtering were applied to Landsat-TM data to divide the Society Cliffs Formation into major stratigraphic subunits. Because iron oxides have been observed at some of the MVT occurrences within the Borden Basin, Landsat-TM data band ratio (3/1) was calculated to highlight the potential presence of iron-oxides as another evidence map. Processed Landsat-TM data and other derived geological evidence maps provided useful indicators for identifying areas of potential MVT mineralization. Weights of evidence and logistic regression were used independently to integrate and generate posterior probability maps showing areas of potential mineralization based on all derived evidence maps. Results indicate that in spite of the lack of important data sets such as stream or lake sediment geochemistry, Landsat-TM data and regional geological data can be useful for MVT mineral-potential mapping.     

基于等值线分布区域树的分层设色图自动生成研究

基于ArcGIS Engine的核心组件功能实现了空间离散点生成等值线,并针对ArcGIS Engine在生成等值线分布区域方面的不足,提出采用等值线分割确定研究区域边界、构建等值线分布区域树的算法,实现了等值线分布区域、拓扑关系构建及高程值的计算,最终实现了分层设色图的自动生成。通过浙江省金华市地下水水位等值线与分层设色图的自动生成试验,表明该文的技术路线是可行的。     

Spatially ordered networks and topographic reconstructions

Abstract

A technique is discussed for obtaining a contour tree efficiently as a byproduct of an operational contouring system. This tree may then be used to obtain contour symbolism or interval statistics as well as for further geomorphological study. Alternatively, the tree may be obtained without the computational expense of detailed contour interpolation. The contouring system proceeds by assuming a Voronoi neighbourhood or domain about each data point and generating a dual-graph Delaunay triangulation accordingly. Since a triangulation may be traversed in a tree order, individual triangles may be processed in a guaranteed top-to-bottom sequence on the map. At the active edge of the map under construction a linked list is maintained of the contour ‘stubs’ available to be updated by the next triangle processed. Any new contour segment may extend an existing stub, open two new stubs or close (connect) two previous stubs. Extending this list of edge links backwards into the existing map permits storage of contour segments within main memory until a dump (either to plotter or disc) is required by memory overflow, contour closure, contour labelling or job completion. Maintenance of an appropriate status link permits the immediate distinction of local closure (where the newly-connected segments are themselves not connected) from global closure (where a contour loop is completed and no longer required in memory). The resulting contour map may be represented as a tree, the root node being the bounding contour of the map. The nature of the triangle-ordering procedure ensures that inner contours are closed before enclosing ones, and hence a preliminary contour tree may be generated as conventional contour generation occurs. A final scan through the resulting tree eliminates any inconsistencies.     

Automation and evaluation of graduated dot maps

Dot mapping is a traditional method for visualizing quantitative data, but current automated dot mapping techniques are limited. The most common automated method places dots pseudo-randomly within enumeration areas, which can result in overlapping dots and very dense dot clusters for areas with large values. These issues affect users’ ability to estimate values. Graduated dot maps use dots with different sizes that represent different values. With graduated dot maps the number of dots on a map is smaller, reducing the likelihood of overlapping dots. This research introduces an automated method of generating graduated dot maps that arranges dots with blue-noise patterns to avoid overlap and uses clustering algorithms to replace densely packed dots with those of larger sizes. A user study comparing graduated dot maps, pseudo-random dot maps, blue-noise dot maps and proportional circle maps with almost 300 participants was conducted. Results indicate that map users can more accurately extract values from graduated dot maps than from the other map types. This is likely due to the smaller number of dots per enumeration area in graduated dot maps. Map users also appear to prefer graduated dot maps over other map types.     

Does base map size and imagery matter in sketch mapping?

Sketch mapping has been an important data collection technique for geographers since the 1960s. Structured sketch mapping requires participants to draw spatial data onto a base map containing cartographic information, in order to assist with spatial referencing. A concern that base map characteristics may influence sketch map content has been raised repeatedly in the research literature. However little scholarly attention has been paid to systematically testing the effect of base maps.This paper aims to test the effects of base map size and imagery on structured sketch maps of avoidance behaviour in university students. Using an experimental design, 272 sketch maps were compared for differences in: sketch map style; the location of collective avoidance hotspots; the extent of the reported area avoided; the number of reported areas avoided; the intensity of avoidance; and the tortuosity of sketch map features.No significant differences were found between base maps in sketch map style or the size, intensity or number of areas avoided. Provision of larger base maps caused respondents to draw more detailed sketch maps. Collective avoidance hotspots shifted location slightly between base maps, probably due to difficulties interpreting aerial photographs.Sketch map content appears to be remarkably robust to changes in base map. Base maps appear to assist respondents with spatial referencing rather than cueing respondents to report specific features.     

一个计算山地地形参数的计算机模式

本文提出了一个虚拟次网格二维差分格式,依此建立了一个计算山地小地形参数(即局地平均坡向、坡度和地形遮蔽角)的通用计算机模式。模式的输入参数为研究地区的拔海高度网格化后的资料、空间格距和网格点数;模式的输出结果为每个格点上的坡向、坡度及沿任一方位上的地形遮蔽角以及一些地形统计值。由此,可较准确、客观地制作出研究山区的坡向、坡度图和地形遮蔽图。经实测验证,模式的计算值与实测值比较吻合。     

等高线节点密度对DEM精度的影响

以西南丘陵地区两种比例尺的地形图为数据源,利用GIS软件平台研究不同等高线节点密度下的DEM精度,旨在揭示节点密度对DEM精度的影响.结果表明:不同节点密度所生成的DEM的高程主要差异区域分布在地形结构线附近;当比例尺为1:2000和1:1万,分辨率分别高于2 m和5 m时,节点的变化对DEM的精度并没有明显影响;分辨率低于2 m和5 m时,其理想的节点密度分别约为1/7个/m和1/12个/m,当大于此节点密度时,增加等高线节点并不能改善DEM的质量,反而会降低DEM的精度.     

基于电子地图兴趣点的城市建成区边界识别方法

城市建成区边界是认识和研究城市的重要基础性信息,也是落实城市功能空间布局、实施界限管控的前提。但是,以往通过夜间灯光的强度、土地覆被或建筑覆盖率等信息获取城市空间范围的方法,由于受到数据精度和尺度限制,对城市社会经济活动的解释性不强,因而存在较大局限性。电子地图兴趣点（POI）作为城市空间分析的基础数据之一,直观且有效地反映了各类城市要素的集聚状况。本文基于POI与城市空间结构和城市要素空间分布的关联性,提出了一种新的通过POI密度分布来判别城市建成区边界的技术方法。为此,开发了Densi-Graph分析方法,用来分析POI密度等值线的变化趋势,在此基础上对城乡过渡地带的阈值识别的方法进行了理论分析,并讨论了单中心圆结构、双中心“鱼眼型”结构、双中心“子母型”结构等各类城市POI密度等值线的生长规律,证明了Densi-Graph分析方法的适用性。较之以往的城市建成区边界识别方法,这种方法的基础数据更加直观可信,分析结果也更加客观。运用这种方法,本文对全国地级以上城市的建成区边界进行了实证分析,探索了城市建成区边界的阈值及其与城市人口规模、城市所在区域之间的关系。     

Mapping the physiography of Michigan with GIS

Abstract

We present a new physiographic map of Michigan, that is also available interactively, online. Only four, small-scale physiographic maps of Michigan had been previously published. Our mapping project made use of a wide variety of spatial data, in a GIS environment, to visualize and delineate the physical landscape in more detail than has been done previously. We also examined many of the unit boundaries in the field, using a GIS running on a GPS-enabled laptop. Unlike previous physiographic maps, the online version of the map enables users to query the criteria used to define each of the 224 boundaries of its 10 major and 91 minor physiographic units. The interactive nature of the online version of the map is a unique enhancement to physiographic maps and mapping. Our study also provides data on the number and types of criteria used to define each of the 224 unit boundaries within the map. Most of our unit boundaries are based on data derived from 10-m raster elevation data and NRCS soils data, e.g., relief, soil wetness, escarpments, landscape fabric, and parent material characteristics. Data gleaned from NRCS SSURGO county-scale soil maps were a strength of the project. [Key words: Michigan, physiography, landforms, soils, GIS, mapping]     

基于GIS的山区年均温分布模拟与制图

针对某些下垫面复杂而气象站(哨)有限的山区,用地理信息系统(GIS)和气温推算数学模型相结合,来获取全域的年均温分布栅格图和等值线矢量图。以龙游县为例,说明了该方法从数学模型、因素图输入、图层格式转换、图幅叠置分析等一系列技术步骤。     

General sky models for illuminating terrains

Sky models are quantitative representations of natural luminance of the sky under various atmospheric conditions. They have been used extensively in studies of architectural design for nearly a century, and more recently for rendering objects in the field of computer graphics. The objectives of this paper are to (1) describe sky models, (2) demonstrate how map designers can render terrain under various sky models in a typical geographic information system (GIS), (3) illustrate potential enhancements to terrain renderings using sky models, and (4) discuss how sky models, with their well-established standards from a different discipline, might contribute to a virtual geographic environment (VGE).

Current GIS hill-shading tools use the Lambertian assumption which can be related to a simple point light source at an infinite distance to render terrain. General sky models allow the map designer to choose from a gamut of sky models standardized by the International Commission on Illumination (CIE). We present a computer application that allows the map designer to select a general sky model and to use existing GIS tools to illuminate any terrain under that model. The application determines the orientations and weights of many discrete point light sources that, in the aggregate, approximate the illumination provided by the chosen sky model. We discuss specific enhancements to terrains that are shaded and shadowed with these general sky models, including additional detail of secondary landforms with soft shadows and more realistic shading contrasts. We also illustrate how non-directional illumination models result in renderings that lack the perceptual relief effect. Additionally, we argue that this process of creating hill-shaded visualizations of terrain with sky models shows parallels to other geo-simulations, and that basing such work on standards from the computer graphics industry shows potential for its use in VGE.     

Comparison of flood hazard assessments on desert piedmonts and playas: A case study in Ivanpah Valley, Nevada

Accurate and realistic characterizations of flood hazards on desert piedmonts and playas are increasingly important given the rapid urbanization of arid regions. Flood behavior in arid fluvial systems differs greatly from that of the perennial rivers upon which most conventional flood hazard assessment methods are based. Additionally, hazard assessments may vary widely between studies or even contradict other maps. This study's chief objective was to compare and evaluate landscape interpretation and hazard assessment between types of maps depicting assessments of flood risk in Ivanpah Valley, NV, as a case study. As a secondary goal, we explain likely causes of discrepancy between data sets to ameliorate confusion for map users. Four maps, including three different flood hazard assessments of Ivanpah Valley, NV, were compared: (i) a regulatory map prepared by FEMA, (ii) a soil survey map prepared by NRCS, (iii) a surficial geologic map, and (iv) a flood hazard map derived from the surficial geologic map, both of which were prepared by NBMG. GIS comparisons revealed that only 3.4% (33.9 km²) of Ivanpah Valley was found to lie within a FEMA floodplain, while the geologic flood hazard map indicated that ~ 44% of Ivanpah Valley runs some risk of flooding (Fig. 2D). Due to differences in mapping methodology and scale, NRCS data could not be quantitatively compared, and other comparisons were complicated by differences in flood hazard class criteria and terminology between maps. Owing to its scale and scope of attribute data, the surficial geologic map provides the most useful information on flood hazards for land-use planning. This research has implications for future soil geomorphic mapping and flood risk mitigation on desert piedmonts and playas. The Ivanpah Valley study area also includes the location of a planned new international airport, thus this study has immediate implications for urban development and land-use planning near Las Vegas, NV.