John R. Weeks

Measuring the Physical Composition of Urban Morphology Using Multiple Endmember Spectral Mixture Models

The application of multiple endmember spectral mixture analysis (MESMA) to map the physical composition of urban morphology using Landsat Thematic Mapper (TM) data is evaluated and tested. MESMA models mixed pixels as linear combinations of pure spectra, called endmembers, while allowing the types and number of endmembers to vary on a per-pixel basis. A total of 63 two-, three-, and four-endmember models were applied to a Landsat TM image for Los Angeles County, and a smaller subset of these models was chosen based on fraction and root-mean-squared error (RMSE) criteria. From this subset, an optimal model was selected for each pixel based on optimization for maximum area coverage. The resultant endmember fractions were then mapped into four main components of urban land cover: Vegetation, Impervious surfaces, Soil, and Water/Shade. The mapped fractions were validated using aerial photos. The results showed that a majority of the image could be modeled successfully with two- or three-endmember models. The validation results indicated the robustness of MESMA for deriving spatially continuous variables quantified at the sub-pixel level. These parameters can be readily integrated into a wide range of applications and models concerned with physical, economic, and/or sociodemographic phenomena that influence the morphological patterns of the city.

Assessing vulnerability to earthquake hazards through spatial multicriteria analysis of urban areas

Assessing urban vulnerability to natural hazards such as earthquakes can be regarded as an ill-structured problem (i.e. a problem for which there is no unique, identifiable, objectively optimal solution). A review of the literature indicates a number of contrasting definitions of what vulnerability means, as well as numerous conflicting perspectives on what should or should not be included within the broad assessment of vulnerability in cities. This paper reports on the findings from a project in which a GIS methodology has been developed to assess urban vulnerability through a spatial analytical procedure. First, we highlight the deficiencies of current GIS approaches to urban vulnerability analysis and discuss the ill-structured nature of the vulnerability problem. We then propose a working definition for vulnerability assessment in which vulnerability is thought of as a spatial decision problem under the conditions of uncertainty. Next, we present a methodology to incorporate this definition into a GIS framework that combines elements from the techniques of spatial multicriteria analysis and fuzzy logic. The application of this methodology is then illustrated with a case study from Los Angeles County. The results suggest that the proposed methodology may provide a new approach for analyzing vulnerability that can add to our understanding of human/hazards interaction.

Revealing the Anatomy of Cities through Spectral Mixture Analysis of Multispectral Satellite Imagery: A Case Study of the Greater Cairo Region, Egypt.

Abstract This paper examines the feasibility of spectral mixture analysis (SMA) in deriving comparable physical measures of urban land cover that describe the morphological characteristics of cities. SMA offers a way of analyzing satellite imagery of urban areas that may be superior to more standard methods of classification. Mixing models are based on the assumption that the remotely measured spectrum of a given pixel can be modeled as a combination of pure spectra, called endmembers. SMA, using four image endmembers (vegetation, impervious surface, soil, and shade), was applied to an IRS‐1C multispectral image in order to extract measures that describe the anatomy of the Greater Cairo region, Egypt, in terms of endmember fractions. The resulting fractions were then used to classify the urban scene into eight classes of natural and human‐built features through a decision tree (DT) classifier. The accuracy of the DT classification was compared to the accuracies of two per‐pixel supervised classifications of the IRS‐1C image employing maximum likelihood (ML) and minimum distance‐to‐means (MDM) classifiers. Overall KAPPA accuracies were 0.88 for the DT classification based on SMA fractions, and 0.60 and 0.45 for the classifications conducted through ML and MDM respectively.

Object-based classification of residential land use within Accra, Ghana based on QuickBird satellite data

A segmentation and hierarchical classification approach applied to QuickBird multispectral satellite data was implemented, with the goal of delineating residential land use polygons and identifying low and high socio‐economic status of neighbourhoods within Accra, Ghana. Two types of object‐based classification strategies were tested, one based on spatial frequency characteristics of multispectral data, and the other based on proportions of Vegetation–Impervious–Soil sub‐objects. Both approaches yielded residential land‐use maps with similar overall percentage accuracy (75%) and kappa index of agreement (0.62) values, based on test objects from visual interpretation of QuickBird panchromatic imagery.

Measuring temporal compositions of urban morphology through spectral mixture analysis: toward a soft approach to change analysis in crowded cities

This paper reports on preliminary results from a study applying the technique of spectral mixture analysis (SMA) to the measurement of temporal changes in the composition of urban morphology in the metropolitan area of Greater Cairo, Egypt, between 1987 and 1998. Although several remote sensing techniques have been used successfully for urban change analysis, most of these focus on change ‘between’ classes measured in a discrete, crisp way through which each pixel is assigned to a label indicating either a change or no change in the class to which the pixel originally belonged. In many major cities, such as Cairo, change also occurs within classes (e.g. vertical growth of buildings, increase in housing density, decrease in open spaces) and is reflected by an aggregation of land cover and urban materials. None of these materials may seem important in isolation. Rather, the significance of these urban land covers arises from the way they interweave with each other to structure the morphology of the urban place. In this paper, a ‘soft’ approach is presented to identify and measure the composition of changing morphology from multi‐temporal, multi‐spectral satellite images. SMA is demonstrated to be capable of deriving spatially continuous variables quantified at the sub‐pixel level. These variables represent measures that can be compared across urban places and at different time periods. They can be integrated readily into a wide range of applications and models concerned with physical, economic and/or socio‐demographic phenomena in the city.

Density of Indoor Tanning Facilities in 116 Large U.S. Cities

BACKGROUND U.S. adolescents and young adults are using indoor tanning at high rates, even though it has been linked to both melanoma and squamous cell cancer. Because the availability of commercial indoor tanning facilities may influence use, data are needed on the number and density of such facilities. METHODS In March 2006, commercial indoor tanning facilities in 116 large U.S. cities were identified, and the number and density (per 100,000 population) were computed for each city. Bivariate and multivariate analyses conducted in 2008 tested the association between tanning-facility density and selected geographic, climatologic, demographic, and legislative variables. RESULTS Mean facility number and density across cities were 41.8 (SD=30.8) and 11.8 (SD=6.0), respectively. In multivariate analysis, cities with higher percentages of whites and lower ultraviolet (UV)index scores had significantly higher facility densities than those with lower percentages of whites and higher UV index scores. CONCLUSIONS These data indicate that commercial indoor tanning is widely available in the urban U.S., and this availability may help explain the high usage of indoor tanning.

Fertility and adaptation: Indochinese refugees in the United States.

Levels of fertility among Indochinese refugees in the United States are explored in the context of a highly compressed demographic transition implicit in the move from high-fertility Southeast Asian societies to a low-fertility resettlement region. A theoretical model is developed to explain the effect on refugee fertility of social background characteristics, migration history and patterns of adaptation to a different economic and cultural environment controlling for marital history and length of residence in the U.S. Multiple regression techniques are used to test the model which was found to account for nearly half of the variation in refugee fertility levels in the United States. Fertility is much higher for all Indochinese ethnic groups than it is for American women; the number of children in refugee families is in turn a major determinant of welfare dependency. Adjustments for rates of natural increase indicate a total 1985 Indochinese population of over one million, making it one of the largest Asian-origin populations in the United States. This remarkable phenomenon has occurred in less than a decade. Implications of these findings for public policy are discussed, focusing on family planning, maternal and child health needs, and the attainment of refugee economic self-sufficiency.

Sachet drinking water in Ghana's Accra-Tema metropolitan area: past, present, and future

Population growth in West Africa has outpaced local efforts to expand potable water services, and private sector sale of packaged drinking water has filled an important gap in household water security. Consumption of drinking water packaged in plastic sachets has soared in West Africa over the last decade, but the long-term implications of these changing consumption patterns remain unclear and unstudied. This paper reviews recent shifts in drinking water, drawing upon data from the 2003 and 2008 Demographic and Health Surveys, and provides an overview of the history, economics, quality, and regulation of sachet water in Ghanas Accra-Tema Metropolitan Area. Given the pros and cons of sachet water, we suggest that a more holistic understanding of the drinking water landscape is necessary for municipal planning and sustainable drinking water provision.

Infant Mortality Among Ethnic Immigrant Groups

The numerically large and growing Indochinese refugee population has been little studied with respect to infant health. It is a population that is young, is experiencing high fertility, late onset of prenatal care, and is characterized by low socioeconomic status. Thus, it presents a high risk profile with respect to infant mortality. Using linked birth and infant death records for the San Diego metropolitan area for the period 1978-85 infant mortality rates (IMRs) were calculated for Indochinese refugee groups from Vietnam, Laos and Cambodia in comparison with other ethnic groups. We found, surprisingly, that Indochinese refugees as a group had an IMR below that for non-Hispanic Whites and substantially below that for Blacks. In general, IMRs for Indochinese refugees were similar to those for other Asian groups. These findings held even after controlling for birth weight and onset of prenatal care. The timing and causes of death suggest areas in which the IMR could drop to even lower levels with improved community outreach programs, especially among refugee groups from Laos (Hmong and Lao) who exhibited the unusual pattern of higher post-early neonatal than early neonatal mortality.

Does Community Context Influence Reproductive Outcomes of Mexican Origin Women in San Diego, California?

An increasing body of literature documenting what has become known as “the Epidemiological Paradox” has shown that some immigrant groups to the United States tend to have healthier birth outcomes than would be expected given their sociodemographic profiles. Furthermore, the children of these immigrants do not seem to enjoy the same advantage in reproductive health that their parents did. This phenomenon, though amply documented in the literature, has not been sufficiently explained. We investigate the role of assimilation in this paradox, and we do so within a spatial framework. We examine the effect of residence in a Mexican enclave in the attenuation of risk of low birth weight (LBW) for Mexican-origin mothers in San Diego County, California. We find that Mexican-origin women do seem to enjoy a reduced risk of giving birth to an LBW baby when they live in a Mexican enclave.