Geography 121

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Geography 121

• Project 3
• NATIONAL MAP DATA

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Digital Elevation Model (DEM)

• Digital elevation models are simply maps showing
  the elevation of land on Earth.
• They are raster images of spot heights (each
  pixel is one height)
• Simplest and most common digital representation
  of topography
• Most DEMs are made by photogrammetry, usually
  from aerial photographs
• They can be used for revealing features on
• the land, such as mountain ranges and bodies
• of water

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Digital Elevation Model (DEM)

• Go to http//edc.usgs.gov/geodata/
• Under 1250,000 Scale Digital Elevation Models
  (DEM) (it should already be up), click on State
• Click on your state
• Find your location of preference, then click
  Compressed to download the file, and save it to
  your hard drive
• Double click your file and unzip it to a location
  on your hard drive
• (if WinZip asks for an extension for the file
  while unzipping, type dem)

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Digital Line Graphs (DLG)

• DLG are digital vector representations of
  cartographic information
• DLG graphs are made up of nodes or points, line
  segments connecting two nodes, and areas formed
  by three or more line segments

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DLG Scales

• Large Scale are124,000 and 125,000 and are 7.5
  minute topographic quadrangles
• Medium Scale are 1100,000 and are 30 by 60
  minute quadrangles.
• Small Scale are 12,000,000 and broken into
  sections or by State

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Use of DLG

• Some of the use of DLG include but are not
  limited to
• Political Boundaries
• Transportation Data
• Significant Manmade Structures
• Hydrography (flowing water, standing water, and
  wetlands)

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DLG Resources

• More information found in the text in Module 3,
  Topic 3, Lesson 5.
• Addition resources for DLG Maps can be found at
  http//edc.usgs.gov/guides/dlg.html

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How To Obtain You DLG Map

• Go to http//edc.usgs.gov/geodata/
• Click on DLG 1100K
• Click on State
• Click on Your State
• And follow the same steps as for your DEM map

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Digital Orthophoto Quarter Quadrangle (DOQQ)

• Raster images of rectified aerial photographs
• Most cover one quarter of a standard topographic
  quadrangle (3.75 square)
• Widely used to edit existing vector and
  planimetric data

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DOQQ Creation and Production

• Aerial Photograph
• Orthorectification
• Scale is constant throughout the image
• Each pixel 1meter on the ground
• Associated with gray levels (255 to 0)
• 0 is black
• 255 is white

Portion of a Digital Orthophoto Quad (DOQ) for
Bushkill, PA Source U. S. Geological Survey.
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Data and Distribution

• Accuracy standards warrant that 90 of well
  defined points be within 20 feet (6.1 meters) of
  their actual positions.
• Positions are verified with the UTM projection
  for the specific zone and verified using the
  NAD83 datum.
• DOQQ files are extremely large MUST DELETE
  AFTER YOU WORK WITH THEM!

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Obtaining DOQQ Images

• Go to EarthExplorer - http//earthexplorer.usgs.go
  v
• Login as GUEST
• Under Spatial Coverage Section enter the
  coordinates of your hometown. You can search for
  hometown coordinates within EarthExplorer
• Select Data Set Under Aerial Photography,
  select both Digital Orthophoto Quadrangle boxes.
• Click Continue, verify your search criteria, and
  click search.
• WAIT UNTIL the STATUS COLUMN SAYS COMPLETE!

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Obtaining DOQQ Images (cont.)

• 7. Browse through results when complete. Click
  Show to view images.
• 8. Pick a single DOQQ and save it to your www
  folder.
• 9. You can put the image itself right in the
  project.
• 10. Metadata can be viewed by clicking on show
  underneath the show all fields column
• NOTE! Pennsylvania Residents can also use the
  PASDA page (http//www.pasda.psu.edu/). Follow
  on-screen prompts to use.

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• Here is an example of a DOQQ image obtained using
  EarthExplorer

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Making Your Map

• Now that you have chosen your maps, it is time to
  put them on a program so you may see them.

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Dlgv32 Pro (Global Mapper)

• The dlgv32 is the program that will put you map
  into a visual context.
• To get to this program, click on start ? programs
  ? Geog 121 ? then on to the dlg32 pro program.

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Loading your map

• To put your map onto this program, simply go to
  file then click on open.
• Click on one of the maps that you downloaded.
• If a window pops up choose the last option, it
  should say USGS/CDED DEM

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Loading your map (cont)

• Then your map should appear on the program.
• When your map is uploaded, hold down alt and
  print screen so you will take a screen shot of
  the program to put on your website.
• If you want to overlay more data on to your map,
  under the file option in the dlg32 program, click
  on select overlay data and select your
  downloaded file.
• Redo all of these steps for the other maps.

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Additional Information

• Project 3 sample available under the lessons tab
  in the Projects folder on ANGEL!
• This Power Point Presentation can be viewed at
  http//www.personal.psu.edu/mhp124/DOQQ_presentati
  on.ppt