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Database of Geographic Information: Topographic Map of Central Arizona
Identifier:220_1
Publication date:2004
Author(s):
Alexander Buyantuyev
Abstract:
This dataset has been created to meet the needs of the research community of Arizona State University. Apart from purely vizualization purposes (i.e. displaying the data on various maps) it can potentially be used for spatial modeling. The data consist of engineering-quality contours, also known as isolines, created from the NED 10-meter Digital Elevation Model subset to the extent somewhat exceeding Cetral Arizona - Phoenix LTER. Contours ( lines connecting points of equal height above sea level) are drawn at 15 meter intervals with the base set at 145 m of elevation. Contours are an exact interpretation of the grid surface model and may sometimes appear blocky looking, may cross, appear to intersect, or form an unclosed branching line. All these are valid engineering-quality interpretations of the elevation surface that cartographers typically modify (smooth) for aesthetic purposes.
Keywords:
SONORAN DESERT, PHOENIX, urban, Elevation, informatics, caplter, Central Arizona Phoenix Longterm Ecological Research, metropolitan area, Arizona, Digital Elevation Model, contours, isolines, topomap, Database Remote Sensing GIS Applications, Project id 1, gis, remote sensing
Temporal Coverage:
1954-01-01 - 1984-01-01
Geographic Coverage:
Geographic Description:Central Arizona Phoenix
Bounding Coordinates:
Longitude:-113.291341 to -111.26736
Latitude:33.909831 to 32.888377
Contact:
Data Manager, Global Institute of Sustainability, Arizona State University,
Global Institute of Sustainability, Arizona State University, POB 875401,TEMPE
caplter.data@asu.edu
Methods used in producing this dataset:
DEM preparation
The U.S. Geological Survey National Elevation Dataset (NED), which is a seamless mosaic of best-available elevation data, was used to prepare the DEM. Three separate areas consisting of multiple USGS quads were obtained from the GIS lab and mosaicked in Erdas Imagine software. The resulting raster was reprojected to the North American Datum 27 UTM Zone 12 coordinate system using bilinear interpolation resampling technique. The final extent was derived by subsetting to the rectangular area that runs from the Gila River on the south to the edge of the uplands (lower border of the rim) on the north. The extent covers parts of Maricopa, Yavapai, Gila, and Pinal counties. In an attempt to produce smoother contours the raster data were subject to two additional processing steps. Sinks were filled in ArcInfo to make sure that a drainage network is continuous. The next step was to adjust Z values so that a contour does no longer pass exactly through a mesh point. This was done by using ArcInfo FOCALSUM function with WEIGHT option. The following 3X3 kernel file was used: .005 .005 .005 .005 .960 .005 .005 .005 .005 Within this neighborhood each value in the initial DEM grid is first multiplied by the corresponding value and then summed up. The sum is then sent to the corresponding cell location (the middle cell) in the output grid
Creating contours
The vector coverage was created in ArcInfo by using CONTOUR function. The interval was set to 15 meters and the base was set to 145.0001 meters. The .0001 offset is an additional approach that is employed to produce smoother contours. Because the offset is very small the accuracy of resulting contours is not significantly affected. An additional attribute, ELEV, was created in the arc attribute table (.aat). It is populated by initial grid values converted into integer format, i.e. rounded to the nearest integer value, and can be used for labeling purposes.
Entities:
Spatial Vector: contour15
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Attributes:
Attribute:FID
Description:Internal feature number.
Attribute:Shape
Description:Feature geometry.
Attribute:LENGTH
Description:LENGTH
Measurement Unit:meter
Attribute:CONTOUR
Description:Elevation in meters from cell values in the input DEM grid
Measurement Unit:meter
Attribute:ELEV
Description:Elevation in meters converted to integer format.
Measurement Unit:meter
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