Showing papers on "Choropleth map published in 1979"
1 Jan 1979
TL;DR: In Tobler's unclassed mapping, the computer is used to create a virtually continuous array of crossed-line shadings from white to black, thus eliminating the need to generalize quantitative area distributions into classes.
Abstract: In Tobler's unclassed mapping, the computer is used to create a virtually continuous array of crossed-line shadings from white to black, thus eliminating the need to generalize quantitative area distributions into classes. Criticism of this method has centered on potential interpretation difficulties for the map user. These and other issues have been examined through subject testing. A preliminary test concerning the relationship between calculated and perceived values for crossed-line shadings showed that people tend to underestimate value differences and an exponent was derived to compensate for this underestimation. A comparative evaluation between unclassed and traditional class-interval methods of choropleth mapping based on critical attributes of choropleth map communication indicate that judgments of both relative and absolute values for individual areas are improved with the unclassed method while there is little difference in the quality of the overall pattern produced by the two methods, at leas...
31 citations
TL;DR: Results lead one to believe that map readers can see and reorganize elements of a no-class map in a consistent and logical fashion, which raises serious questions regarding the relevance of class generalization on the grounds of cartographic communication.
Abstract: Readers were asked to visually categorize the areas of high, medium, and low densities shown on a continuously shaded choropleth map The perceived patterns replicate closely the three-class categorization derived from an optimum statistical generalization These results lead one to believe that map readers can see and reorganize elements of a no-class map in a consistent and logical fashion This raises serious questions regarding the relevance of class generalization on the grounds of cartographic communication
26 citations
1 Jan 1979
TL;DR: Tobler et al. as mentioned in this paper introduced a computer-assisted method to produce choropleth maps without class intervals by means of continuous-tone map symbol variation, including an improved legend, an alternative data-value map symbol allocation, and area symbols with pattern variation complementing cross-hatch line symbolism.
Abstract: Conventional choropleth maps are constructed with class intervals whereby a given map symbol represents a range of data values in a distribution. Tobler recently has introduced a computer-assisted method to produce choropleth maps without class intervals by means of continuous-tone map symbol variation. Three design modifications for such continuous-tone choropleth maps include an improved legend, an alternative data-value map symbol allocation, and area symbols with pattern variation complementing cross-hatch line symbolism.
17 citations
1 Aug 1979
TL;DR: A recent joint project undertaken by the NASA/Goddard Space Flight Center and the Bureau of the Census to demonstrate the potential of graphic information display technology for the rapid delivery and effective display of Federal statistics is described.
Abstract: Governmental decision makers require an increasing variety and volume of information in order to formulate effective policies, plans, and legislation. Moreover, rapid access to this broad body of information is critical to timely and effective governmental action. This paper describes a recent joint project undertaken by the NASA/Goddard Space Flight Center and the Bureau of the Census at the request of the Executive of the President to demonstrate the potential of graphic information display technology for the rapid delivery and effective display of Federal statistics. This project resulted in the development of a prototype Domestic Information Display System which was demonstrated to President Carter, members of Congress, and their respective staffs in June 1978.The Domestic Information Display System is an interactive, menu-driven software system which produces single and bivariate choropleth maps of socio-economic data by county at the national and state level, and by census tract for Standard Metropolitan Statistical Areas (SMSA's). Selected subareas of national and SMSA maps may be dynamically enlarged to show greater detail. Histogram displays may be selected to show statistical as well as geographic structure.The system is minicomputer-based and utilizes the image manipulation capabilities of a raster-scan color graphics terminal designed at NASA/Goddard as part of the Atmospheric and Oceanographic Information Processing System (AOIPS) which was adapted to demonstrate the potential of a Domestic Information Display System. The system is highly interactive and can produce a color map display within seconds of the selection of a data item from a menu.This paper discusses the operation of the Domestic Information Display System, presents sample output products, and describes in detail the software and hardware organization through which the system flexibility and rapid response were achieved.
9 citations