This paper aims to develop a simple technique for defining employment concentrations, suitable for application to any large North American urban area, and to implement it for a major area. Following a review of earlier work, the 1990 distribution patterns of population, resident workers, and jobs in greater Los Angeles are mapped, summarized in tabular form, and compared. After a consideration of alternative approaches, employment concentrations are delineated using census tracts, with the 1990 employment/residence ratio as chief criterion, rather than job density. Of 120 concentrations defined, 11 have more than 100,000 jobs each and 28 have at least 50,000. Downtown Los Angeles, still the region's largest concentration, now is rivaled by the relatively new Irvine. Comparable 1980 data show job growth in most concentrations, although increases Downtown have been modest. The industry profiles of the largest concentrations vary widely, especially as to the significance of manufacturing, which dominates some concentrations but is relatively unimportant in others. The data are inconclusive as to whether jobs in the region became more or less concentrated during the 1980s. The paper also questions two of Garreau's "edge cities" criteria by showing that most such developments in the Los Angeles region are not wholly new and already existed as job concentrations 30 years ago.

Lists of the world's most populous urban areas are surprisingly inconsistent in standard reference sources. These even disagree about which area is the world's largest. We first review the differences found in lists of the 20 largest areas reported by several unofficial sources and by the United Nations. We then demonstrate that variations in the populations and rankings stem mostly from differences in concepts and geographic definitions, and identify six different types of definition in the UN's list. We also offer a set of consistently defined metropolitan areas based on stated guidelines. Case studies for Tokyo, Mexico City, Los Angeles and Beijing include maps to elucidate the administrative areas and statistical definitions in use in each of these urban areas, and illustrate how the varying definitions yield different population totals. We conclude by comparing our consistently defined metropolitan areas with the UN's list of largest urban agglomerations. Copyright (c) 2009 by the Royal Dutch Geographical Society KNAG.

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