It was the largest and most accurate census to that time. Using statistically reliable estimates produced from exhaustive follow-up surveys, the Bureau's permanent staff determined that the final count was accurate to within 1.6 percent of the actual number (although the count was less accurate for young and minority residences than it was for older and white residents). A mostly-temporary staff of over 800,000 was needed to visit the remaining households, and to produce the final count of 281,421,906. Of the 116 million households to which questionnaires were sent in 2000, 72 percent responded by mail. The Census Bureau then began to distribute questionnaires by mail. population had reached 179 million, it was no longer practical to have a census taker visit every household. They counted some 3.9 million individuals, although as then-Secretary of State, Thomas Jefferson, reported to President George Washington, the official number understated the actual population by at least 2.5 percent (Roberts, 1994). Marshals and 650 assistants conducted the first U.S. These are fun, thought provoking exercises to help you better understand the ideas presented in the chapter. Take a minute to complete any of the Try This activities that you encounter throughout the chapter. use quantile and equal interval classification schemes to divide census attribute data into categories suitable for choroplethic mapping.explain the differences between counts, rates, and densities, and identify the types of map symbols that are most appropriate for representing each and.discriminate between different levels of measurement of attribute data.use metadata and the World Wide Web to assess the content and availability of attribute data produced by the U.S.Students who successfully complete Chapter 3 should be able to: It also considers how the characteristics of attribute data influence choices about how to present the data on thematic maps. This chapter explores the characteristics of attribute data used for thematic mapping, especially attribute data produced by U.S. The thematic map reveals spatial patterns that the data themselves conceal. To gain a sense of how effective this thematic map is in transforming data into information, we need only to compare it to a list of population change rates for the more than 3,000 counties of the U.S. population changed, by county, from 1990 to 2000. The effective use of graphic symbols is an important component in the transformation of geographic data into useful information.Ĭonsider the map above (Figure 3.1.1), which shows how the distribution of U.S. ![]() Over the past 100 years or so, cartographers have adopted and tested conventions concerning symbol color, size, and shape for thematic maps. Abstract graphic symbols must be devised that depict, with minimal ambiguity, the quantities and qualities that give locations their meaning. ![]() Representing the attributes of locations on maps is sometimes not so straightforward, however. Notwithstanding the intricacies of map projections, it is a fairly straightforward matter to plot points that stand for locations on the globe. Thematic maps are among the most common forms of geographic information produced by GIS.Ī flat sheet of paper is an imperfect, but useful, analog for geographic space. Maps created specifically to highlight the distribution of a particular phenomenon or theme are called thematic maps. Many maps, however, are subsets of available geographic data that have been selected and organized in response to a particular question. All maps, but especially so-called reference maps made to support a variety of uses, can be defined as sets of symbols that represent the locations and attributes of entities measured at certain times. Maps are both the raw material and the product of GIS. In this chapter, we'll take a closer look at how attributes are measured and represented. ![]() I mentioned, but did not explain, that attribute data also are specified with reference to measurement scales. Coordinate systems, remember, are formed by juxtaposing two or more spatial measurement scales. In Chapter 2, we compared the characteristics of geographic and plane coordinate systems that are used to measure and specify positions on the Earth's surface.
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