Spatial data sets and map projections: An analysis of distortion.
Item
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Title
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Spatial data sets and map projections: An analysis of distortion.
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Identifier
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AAI9917681
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identifier
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9917681
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Creator
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Mulcahy, Karen Aileen.
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Contributor
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Adviser: Keith C. Clarke
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Date
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1999
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Language
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English
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Publisher
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City University of New York.
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Subject
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Geography | Environmental Sciences
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Abstract
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The depiction of our planet in digital form is at the core of regional and global research efforts. When the size of a study area is minute compared to the size of the earth, an insignificant amount of distortion is introduced during map projection transformation; however, when the area of interest is broad, significant distortion occurs. When raster spatial data sets are transformed by map projections, the actual data values may change significantly, reducing the quality of the data set.;This study explores the changes occurring within regional or global raster data sets as a result of map projection transformations. The methodology consists of tracking pixel loss and pixel duplication separately through the application of new metrics called PD and PL created for this purpose. The spatial extent of this analysis is continental and greater. The world map projections examined are primarily the equal area pseudocylindricals. Azimuthal projections were employed for examination of continental data sets. The Mollweide and Sinusoidal projections are of particular interest as the component projections of the Goode Homolosine projection in use by the US Geological Survey for release of global data sets.;The pseudocylindrical projections show complex behaviors of PL and PD with both pixel loss and duplication occurring simultaneously. Based on the PL and PD results there is an inverse relationship between angular distortion and pixel distortion on the pseudocylindrical projections. In addition, the examination of pixel value changes using PL and PD indicate that distortion patterns on the azimuthal projections are influenced heavily by the angular changes occurring in the graticule. The transformation of raster spatial data sets of large extent by map projections is often an invertible process with current technologies and algorithms.;This research challenges basic cartographic theory regarding map projection distortion. Further research will be needed to define the full set of changes and basic map projection guidelines will need to be updated to include the recommendations from this research. Cartographic education, spatial data users, data producers and spatial data standards are all impacted by these results.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
