National Map Data

1. Project 3: Finding, Retrieving, and Viewing National Map DataRenee deSibour, Kyle Haug, Meredith Hill & Will Harris

2. National Map Data • Topographic maps • Show and name visible characteristics • Show political and administrative boundaries • Map Series • Many different maps put together to form series

3. US National Map • Late 19th Century • Scales used • 1:250,000 • 1:100,000 • 1:63,360 • 1:24,000 • Total 53,838 maps to cover 48 states, Hawaii, and US Territories • 50 years to complete, finished in 1992

4. Three types of National Map Data • Digital Elevation Model (DEM) • Digital Line Graph (DLG) • Digital Orthophoto Quarter Quadrangle

5. Digital Elevation Model • Rastor representation of a terrain surface that is a data product of the U.S. Geological Survey • Contours are useful for depicting terrain, but not as useful to calculate volume, slope, and aspect, which are all often sought after elevation data • Rastor elevation uses a regularly spaced grid to calculate these data which is much easier to do • Another name for rastor elevation data is Data Elevation Models

6. All types are derived from aerial photos • Level 1 DEM • produced photogrammetrically • Level 2 DEM • consist of elevations interpolated from Digital Line Graph (DLG) hypsography data • from digital contours that have been vectorized from scanned topographic maps. • Level 3 DEM • interpolated from integrated DLG hypsography, hydrography, ridge and break lines, and other data.

7. Scale of DEM • Most detailed USGS DEMs (correspond to 1:24,000 on a topographic map) have grid lines spaced 10 meters apart • Most common are ones spaced 30 meters apart

8. Data Quality • Evaluate the accuracy by checking elevations of 28 points within the quadrangle they have measured • Minimum accuracy requirements vary with the most widely used one being that a 7.5 minute DEM (1:24,000 on a topographic map) can be expected to be accurate to within about 3 meters

9. DEM Project – Steps to find a DEM • Click on the last link of the project citations (http://edc.usgs.gov/geodata/) • Click on data set 1:24K DEM (top of site) • Go to first website under #1 (http://gisdatadepot.com/dem) • Click on “DOWNLOAD DEM DATA HERE” under GeoCommunity DEM Resources • Pick your state and click on it • Pennsylvania

10. Steps to find a DEM (cont.) • Pick your county • Dauphin • Click on “DIGITAL ELEVATION MODELS- 24K” (first link) • Pick your city and click on the green box to download your DEM • Harrisburg, East • There will be at least two different links to chose from to download the DEM • Click on the first link (consists of a “#.DEM.SDTS.TAR.GZ (10 meter)”) • Click on save and then choose to save the file onto your ZIP disk • Open dlgv32 Pro from Start menu • Then “File” and “Open as new” and locate the saved file

11. Answers for questions • Area covered by DEM • Harrisburg, Pennsylvania • Where was data acquired • from the website http://gisdatadepot.com/dem • Resolution of DEM • 1:24K • Software used to create image • DLGV32PRO • Comments on landforms • northwest corner= mmountain chain (elevation- 400m) • southwest corner= edge of body of water (elevation- 85m) • map consists mostly of elevation from 110m- 160m (green area) with several streams of slightly lower elevation

12. Digital Line Graphs (DLG) • Multi-layered • Vector representations of the boundaries, transportation routes, hydrography, hypsography, and other features shown on USGS topographic maps ** "Hypsography" refers to the measurement and depiction of the terrain surface, specifically with contour lines.

13. DLG (cont.) • Every digital contour in a DLG hypsography layer consists of a set of point features that share two common attributes: an elevation and an identification code. • The preferred method for producing digital layers is to: • separately digitize each category of features shown on USGS topographic maps • every digital feature represented in the file is attributed with a code number that identifies that feature uniquely, and as a member of a particular feature category

14. Data Quality • DLGs conform to National Map Accuracy Standards • Elevations of well-defined points are warranted to be within one-half contour interval of their actual elevation. • The contour interval of topographic maps varies by quad sheet. • At 1:24,000 scale, the contour interval often 20 feet. • Elevations of well-defined points in most DLGs can be assumed to be accurate to within ±10 feet.  

15. Data Quality (cont.) • Logical consistency --lines begin, end, and connect to one another at nodes --DLG files are warranted to be free of topological defects.

16. Spatial Reference Information • Elevations are expressed in feet, relative to the National Geodetic Vertical Datum of 1929. • Locations are specified in the UTM coordinates of the local zone.

17. Distribution • USGS maintains DLGs at three scales: small (1:2,000,000); intermediate (1:100,000), and large (1:24,000). • At 1:24,000 (7.5’ by 7.5’), coverage remains unfinished • Complete coverage is planned. • Use the USGS Status Graphics pages http://mapping.usgs.gov/www/products/status.html to discover whether the DLGs you want are available for your area of interest.

18. DLG Project – Steps to find a DLG • To FIND the data for your area of interest, click on the last link from the sources list. It says “Data Download” http://edc.usgs.gov/geodata/ • Select “1:24K DEM” from menu at top . • Select GeoComm Intl. Corp. hyperlinkhttp://gisdatadepot.com/dem • From “Topics” menu on left, select “Download Data” • Choose which state you are interested in obtaining data for. • A new window should open up with a listing of each County. Click on the county that your area of interest is located in. • A listing of various downloadable data for the area will appear.

19. Steps to download a DLG • To DOWNLOAD, click on the National Map data that you want to download, paying attention to what resolution the data is in. You can download both the DEM and DLG data from here. • For DLG data: • Choose “Digital Line Graphs (DLG) 24K” from menu • Find your area of interest and download the free data using the green button • Note: There may be multiple files of data to download. Choose up to four files to download from the main download page. These files are just the different layers that will be utilized later when viewing the data. Do not open the files after downloading if asked.

20. Steps to view DLG • To VIEW the data, open up the program “dlgv32 Pro”. --It should be located under: Start  Programs  USGS  dlgv32 Pro in the labs here. Note: If you choose to do this at home, you can download the software from the website, which is located at: http://mcmcweb.er.usgs.gov/drc/dlgv32pro/).

21. Steps to view DLG (cont.) • Choose: File  Open as new, and locate where you stored the downloaded information. • Highlight up to four entities of DLG files and click Open. A map should appear. By clicking on the “Open Control Center” button at the top, you can see which entities are entered. Here, you can choose to hide or show them in the map. Make sure you know which entities are represented in the map so you can comment on them. • By choosing the “pick tool” (button with cursor on it) from the menu at the top, you can now click on your map to see element information about each entity. • Once you are satisfied with your map, do a Screen Capture, which is Alt+Print Screen and then paste to desired location.

22. Digital Orthophoto Quarter Quadrangle (DOQQ) • Raster images of rectified aerial photographs • Electronically scanned then “orthorectified” • Image is warped to adjust for elevation • Scale is uniform throughout image

23. DOQQ – Data Quality • Confirm to National Map Accuracy Standards • 90% of well-defined points are within 20 ft of actual position • Most inaccuracies occur during rectification

24. DOQQ – Entities and Attributes • Each pixel on DOQQ = 1 m on ground • Each number stands for attribute • 0 = black • 255 = white • Shades between are grays • Available for 80% of 48 States

25. Steps to find a DOQQ • Go to http://geonames.usgs.gov • Click on “United States and Territories” • In the box below, put in the town or city you are using • Select the state • Click on “Send Query”

26. Steps to download a DOQQ • Click on the city or town you are using • Scroll down and click on “View USGS Digital Orthophoto Quadrangle (DOQ) • Click on the “download” at the top • Right click on the image and select “Save Picture As”

27. Steps to download DOQQ (cont.) • Also, click on the GIS World Coordinates under World File: • Go to file, select “Save As” • Go to “Save as Type” and select “Text File” • Go to “File Name” and add “.jgw” at end of name • Save

28. Steps to view a DOQQ • Go to U.S. Geological Survey under “Programs” • Open dlgv32Pro • Click on the “Open as New” under File • Open the JPEG • Will receive an error message, click OK • Click on .jgw file, click open, click OK • Select the file and open the picture • Select the USGS World File

29. Conclusion • To make up National Map • High resolution digital orthoectified imagery • High resolution surface elevation data • Vector hydrography, transportation and boundary data • Land characterization data (raster) • Geographic names • Originally based on available data, but as technology increases more accurate data will be available.

30. Conclusion • This Power Point presentation is available at: http://www.personal.psu.edu/mah339