Maheswari. Visvalingam

Bio: Maheswari. Visvalingam is an academic researcher from University of Hull. The author has contributed to research in topics: Generalization & Heuristics. The author has an hindex of 7, co-authored 10 publications receiving 367 citations.

Line generalisation by repeated elimination of points

Abstract: This paper presents a new approach to line generalisation which uses the concept of 'effective area' for progressive simplification of a line by point elimination. Two coastlines are used to compare the performance of this, with that of the widely used Douglas-Peucker, algorithm. The results from the area-based algorithm compare favourably with manual generalisation of the same lines. It is capable of achieving both imperceptible minimal simplifications and caricatural generalisations. By careful selection of cut-off values, it is possible to use the same algorithm for scale-dependent and scale-independent generalisations. More importantly, it offers scope for modelling cartographic lines as consisting of features within features so that their geometric manipulation may be modified by application- and/or user-defined rules and weights. The paper examines the merits and limitations of the algorithm and the opportunities it offers for further research and progress in the field of line generalisation.

The Signed Chi-square Measure for Mapping

Abstract: When interest extends beyond purely univariate considerations, there is no fixed rule governing the ordering of spatial samples for mapping and statistical analysis. Ratios and numerical differences have conventionally been the basis for comparing samples. As both these are known to be influenced by variations in sample size, they are unsuitable for the comparison of demographic samples which vary greatly in size. Where necessary, the effect of sample size can be accommodated by a modified form of the X2 test statistic which is described in this paper.

Implications of Weighting Metrics for Line Generalization with Visvalingam's Algorithm

Abstract: Visvalingam's algorithm was designed for caricatural line generalization. A distinction must be made between the algorithm and its operational definition, which includes the metric used to drive it. When the algorithm was first introduced, it was demonstrated using the concept of the effective area of triangles. It was noted that alternative metrics could be used and that the metrics could be weighted, for example to take account of shape.Ordnance Survey (Great Britain) and others are using Visvalingam's algorithm for generalizing coastlines and other natural features, with complex parameter-driven functions to weight the original metric. This paper shows how free software and data were used to scrutinize the implications of one of Matthew Bloch's simple and transparent weighting functions. The results look promising, when compared with manually produced mid and small-scale maps; and encourage further research focussed on weighting functions and related topics, such as self-intersection of lines and model...

Maps from Sparse Geospatial Data Tiles

Abstract: Utilizing the structure and methods of the invention herein when loading geographic vector data, the average time to load all necessary geographic data needed for one rendered map to the next will be greatly reduced - the loading time reduction will be especially large when pan and zoom operations are the main transitions from one rendered map to the next. The invention uses tiles of stored geographic data available at some scales to generate maps having several scales, including but not limited to the scales of the stored data. The geographical data is organized in a tile-tree in which different tiles contain approximately the same amount of data. This is accomplished by a data generation process that packs details higher in the tree for areas where the data density is low.

System and method for abstracting and visualizing a route map

Abstract: A system and method for making computer-generated maps includes a different scale factor for each road in a route The scale factors are used to optimize the route map against a target function that considers factors such as the number of false intersections in the route and the number of roads falling below a minimum length threshold A refinement technique such as simulated annealing is used to find a solution to the target function Each road in the scaled map is rendered to provide a finished product having the appearance of a hand-drawn map The finished product includes context roads that intersect the main route but are not part of the main route Furthermore, the hand-drawn map is optimized to the characteristics of the viewport used to visualize the map

Effect of GIS Learning on Spatial Thinking.

Abstract: A spatial-skills test is used to examine the effect of GIS learning on the spatial thinking ability of college students. Eighty students at a large state university completed pre- and post- spatial-skills tests administered during the 2003 fall semester. Analysis of changes in the students' test scores revealed that GIS learning helped students think spatially. These improvements were the result of the connection between students' GIS activities and experiences and the tested spatial thinking skills. Strong correlations were observed between the participants' spatial thinking and their achievement in the GIS course.

World population in a grid of spherical quadrilaterals.

Abstract: We report on a project that converted subnational population data to a raster of cells on the earth. We note that studies using satellites as collection devices yield results indexed by latitude and longitude. Thus it makes sense to assemble the terrestrial arrangement of people in a compatible manner. This alternative is explored here, using latitude/longitude quadrilaterals as bins for population information. This format also has considerable advantages for analytical studies. Ways of achieving the objective include, among others, simple centroid sorts, interpolation, or gridding of polygons. The results to date of putting world boundary coordinates together with estimates of the number of people are described. The estimated 1994 population of 219 countries, subdivided into 19,032 polygons, has been assigned to over six million five minute by five minute quadrilaterals covering the world. These results are available over the Internet. The grid extends from latitude 57°S to 72°N, and covers 360° of longitude. Just under 31% of the (1548 by 4320) grid cells are populated. The number of people in these countries is estimated to be 5.6 billion, spread over 132 million km 2 of land. Extensions needed

Cartography without ‘Progress’: Reinterpreting the Nature and Historical Development of Mapmaking

Abstract: This paper extends the current critique of cartography's empiricist presuppositions to the nature of cartography as a practice. After exploring the relevant aspects of empiricist cartography - the manner in which geographic data are treated as constituting a single, monolithic database and the reliance upon a linear and progressive view of cartographic history - a new interpretation of cartography's nature and of its history are presented. Cartography should be seen as a complex amalgam of cartographic modes rather than as a monolithic enterprise. Each mode comprises a set of cultural, social, and technological relations which determine cartographic practices. This conception is applied to modern European cartography in the period between 1500 and 1850, when mapmaking appeared to progress from being an art to being a science (the 'cartographic reformation'). Approaching this period without prior assumptions of progress reveals that cartography's reformation is a myth created by our misunderstanding of the...