GEOG 121 Project 3:
Finding, Retrieving, and Viewing National Map Data


DAVID BARLEY
Digital Elevation Model (DEM)

  • This DEM represents my hometown, Elizabethtown, Pennsylvania.  It covers the area between 76.625° and 76.5° west longitude, and 40.125° and 40.25° north latitude. This DEM was one of the 1:24K DEMs acquired from the USGS, through PASDA. Its resolution is 10-meters. The DEM was imported into the USGS's dlgv32 Pro software, and then captured using a screenshot.  The goal was consistency between the DEM and the DLG as I kept the same sizes to provide easy reference between the two. 

  • Information about this DEM was obtained through metadata, also available on PASDA.

  • The quickest observation that I made when viewing the DEM is the clear visibility of the built-up roadways. State route 283 runs from the lower right corner to the middle left section of the DEM and you can make out the individual interchanges and bridges on the highway.  There is also a quarry visible south of Elizabethtown, closer to Mount Joy.  Each of the two ridges in Elizabethtown have roads running on top of them, as well.  The upper ridge gets steeper and hillier as it progresses into Lebanon County (the northeast). But Elizabethtown itself is mostly concentrated between the two most visible roadways in the lower-left corner of the DEM.

    • Digital Line Graphs (DLG)

  • This DLG covers the same area as the DEM above: Elizabethtown, PA, Mount Joy and Rapho Townships. The bounding coordinates are the exact same as the DEM. The DLG was obtained through USGS. Since the boundary and hydrography data in and around Elizabethtown is not that complex or significant, I chose to superimpose three sets of transportation data in this DLG. I imported the data files into the dlgv32 Pro software again, and used a screenshot to capture this image.

  • I find the transportation system to reveal a lot of the intricacies visible in the DEM image (two above).  State Route 283 was built in the 1960's and 1970's as a bypass to Route 230, which goes through the heart of Elizabethtown and Mount Joy.  When comparing the DLG to the DEM, it is clear to see that the roadbed for 283 had to be built up in areas, especially northwest of the second ridge.  What I find interesting is that Interstate 76 does not seem to have as much of a topographical impact as Route 283 does, despite being a more significant roadway.  Finally, the railroads have been built alongside the ridges and that is evident from comparing the DEM and the DLG.

    • Digital Orthophoto Quarter Quadrangle (DOQQ)

  • The area covered by the DOQQ is less than that of the DEM and DLG; it focuses more strictly on Elizabethtown and the area southwest instead of east. I acquired the DOQQ and corresponding data at PASDA. This DOQQ is dated April 08, 1999.  I downloaded the DOQQ file (rather portly in size) and, after importing it into the dlgv32 Pro software, scaled it down to a *.gif image and captured it in a screenshot.

  • Information about this DEM was obtained through the DOQQ's metadata, also available on PASDA.

  • The DOQQ reveals everything that was evident in the DLG file; that the transportation data corresponds to major roadways in town and also that the buildup of roadways is visible even from this height.  Farmland is the prevailing feature east of Elizabethtown, and the rolling hills can actually be easily located on the DOQQ after comparing the shape of each plot of farmland with the location of the hills on the DEM.  The first dark red ridge can be traced along a roadway in Southern Elizabethtown, and incidentally, that road is named Ridge Road.  Forests are thick in the northeast area of the DOQQ on the northern side of the ridge.  Also barely visible through the middle of town is the small Conoy Creek, which is indicated by a thin, winding line of trees nestled in between the downtown houses.

    • Sources

    DiBiase, David (2004) Understanding Geographic Data. Module 3: Aerial Photographs and Planimetric Data, and Module 4: Elevation Data. ESRI Virtual Campus http://campus.esri.com Accessed October 2004.
    The Pennsylvania State University and Pennsylvania Geospatial Information Council (2004) Pennsylvania Spatial Data Access. http://www.pasda.psu.edu Accessed 19 October 2004.
    United States Geological Survey (2004) dlgv32 Pro Viewing Software. http://mcmcweb.er.usgs.gov/drc/dlgv32pro/ Accessed 18 October 2004.
    United States Geological Survey (2004) Geographic Names Information System. http://geonames.usgs.gov Accessed 19 October 2004.
    United States Geological Survey (2004) USGS Geographic Data Download. http://edc.usgs.gov/geodata/ Accessed 18 October 2004.