Effective Graphic Features for Multivariate Symbol Mapping

Abstract

Various patterns of cartographic multivariate symbols (MSs) have been developed to work efficiently with objective symbol mapping. One such MS pattern is composed of a graph that uses spatial data to represent statistical data. A preliminary study revealed major problems with users’ perceptions and understanding of the symbol. These problems present obstacles to the presentation objectives. We are therefore interested in studying the human factors that contribute to the visual perception of graph symbols. We predict that the graph symbols currently in use are too complex for viewers to fully understand what they are intended to represent. This research aims to study the mechanisms and behaviours of human visual perception that are necessary to understand cartography MSs and to determine a more effective prototype symbol that presents and conveys information to viewers more efficiently. The prototype design is based on a basic cartographic symbol and includes the characteristics and properties of the original patterns of graph symbols via a study of their pros and cons. Graphic structures and properties were modified to create a more effective symbol.     

基于ArcGIS的矿山资源遥感监测符号库的建立

在矿产资源开发多目标遥感调查与监测项目中,ArcGIS自带的符号库已远不能满足专业需求,须建立新的专业符号库。本文研究ArcGIS符号管理器(Style Manager)及Font Creator 5.0字体编辑器制作符号的方法。针对某矿山区域,建立了矿产资源开发多目标遥感调查与监测专题符号库,并基于ArcGIS Engine和VB.net编程方法,实现地图点、线、面要素的自动符号化显示与管理功能。     

国外地图符号表示差异研究

列举不同国家地图符号表示差异的基础上,确定从视觉变量理论的角度出发对地图符号表示差异进行研究.以色彩视觉变量为例,分析不同国家在色彩使用上的差异是由不同的文化观念造成的.在此基础上探究不同国家地图符号上的差异来源于地图设计者的空间认知能力,即认知结构上的差异.文中设计了地图符号对照表,以此建立国外地图符号与我国符号的对应关系,易于操作,直观明了.     

Visual clutter reduction in zoomable proportional point symbol maps

ABSTRACT

Proportional point symbols are commonly used in map displays. However, when such displays are zoomed out, the available map space shrinks and consequently symbols overlap and the display suffers from visual clutter. Therefore, solutions are needed to reduce visual clutter in zoomable map displays that contain proportional point symbols. The authors add to the body of knowledge through the investigation of the performance of three solutions: aggregation of unit areas, the displacement of overlapping symbols, and modified symbolization; four variations of modified symbolization are examined in detail. The original study begins with a consideration of the strengths and weaknesses of the solutions, with an emphasis on information loss. Thereafter, user sessions with 165 participants are arranged to gain empirical evidence of the performance of the solutions. The results reveal that although participants zoom out the map to zoom levels that implement visual clutter reduction techniques, they tend to zoom in the map and pan it to examine specific areas. Moreover, they willingly use the map with aggregated unit areas in cases when the solution facilitates task accomplishment. A certain amount of skepticism attaches to the solution that displaces overlapping symbols.     

On the inverse dynamo problem in a simplified mean-field model

Inverse dynamo theory seeks to gain information about the motion of a liquid conductor from measurements of the magnetic field in the surrounding vacuum. We consider here a highly simplified model problem, namely a steady α²-dynamo in plane geometry with an α-field varying only in the z-direction normal to the conductor–vacuum interface. Based on perturbation theory about constant-α solutions, we find as many integral conditions on α(z) as modes are present in the vacuum field. This result is corroborated by the complete solution of a special case.     

Inverse dynamo problem in a cylinder

An inverse dynamo problem is presented in which we search for either kinematic dynamos which produce the same external magnetic fields or an invisible dynamo. The existence of flows which produce the same external magnetic fields is proved. However, we have not found general conditions necessary for such kind of dynamos. An “invisible dynamo” operates in an electrically conducting region surrounded by vacuum and generates a magnetic field trapped in the electrically conducting region so that no magnetic field exists in the vacuum. Invisible magnetic decay modes exist in cylinders, but no invisible growing field supported by the dynamo mechanism has been found.     

Exploratory analysis of the interrelations between co-located boolean spatial features using network graphs

Visual data mining of spatial data is a challenging task. As exploratory analysis is fundamental, it is beneficial to explore the data using different potential visualisations. In this article, we propose and analyse network graphs as a useful visualisation tool to mine spatial data. Due to their ability to represent complex systems of relationships in a visually insightful and intuitive way, network graphs offer a rich structure that has been recognised in many fields as a powerful visual representation. However, they have not been sufficiently exploited in spatial data mining, where they have principally been used on data that come with an explicit pre-specified network graph structure. This research presents a methodology with which to infer relationship network graphs for large collections of boolean spatial features. The methodology consists of four principal stages: (1) define a co-location model, (2) select the type of co-association of interest, (3) compute statistical diagnostics for these co-associations and (4) construct and visualise a network graph of the statistic from step (3). We illustrate the potential usefulness of the methodology using an example taken from an ecological setting. Specifically, we use network graphs to understand and analyse the potential interactions between potential vector and reservoir species that enable the propagation of leishmaniasis, a disease transmitted by the bite of sandflies.     

The variable projection method for waveform inversion with an unknown source function

This paper compares three alternative algorithms for simultaneously estimating a source wavelet at the same time as an earth model in full‐waveform inversion: (i) simultaneous descent, (ii) alternating descent and (iii) descent with the variable projection method. The latter is a technique for solving separable least‐squares problems that is well‐known in the applied mathematics literature. When applied to full‐waveform inversion, it involves making the source wavelet an implicit function of the earth model via a least‐squares filter‐estimation process. Since the source wavelet becomes purely a function of medium parameters, it no longer needs to be treated as a separate unknown in the inversion. Essentially, the predicted data are projected onto the measured data in a least‐squares sense at every function evaluation, making use of the fact that the filter estimation problem is trivial when compared to the full‐waveform inversion problem. Numerical tests on a simple 1D model indicate that the variable projection method gives the best result; actually producing results in quality that are very similar to control experiments with a known, correct wavelet.     

反演模型分辨率的估算方法

反演问题的时空间分辨率或称时空分辨长度是评估模型精细程度的重要参数,决定了该模型应用的范围和价值,但是分辨长度估算却是比反演更复杂和麻烦的数学问题。除了层析成像中广泛利用理论模型恢复试验定性提取空间分辨长度外,通过求解分辨率矩阵可定量获得分辨长度。通过矩阵操作给出的分辨率矩阵包括三类：直接分辨率矩阵、正则化分辨率矩阵和混合分辨率矩阵。这三类矩阵包含了反演本身不同侧面的信息,因此在一个反演应用中,同时提供这三类分辨率矩阵可更全面地评估反演模型分辨率分布。最近An（2012）提出了从大量随机理论模型及其解中统计出分辨率矩阵的方法。这种分辨率矩阵是从模拟真实反演实验的输入和输出模型中通过反演得到的,因此这种分辨率矩阵更能反映整个反演所涉及到的更多因素和过程;同时由于这种分辨率矩阵计算过程无需进行矩阵操作且不依赖于具体正演和反演方法,因此可以被应用于更普遍的反演问题。实际应用证明统计分辨率分析方法适用于对二维和三维层析成像反演模型进行分辨率分析。