Fundamentals of GIS Lecture 16: Data Input I: Selected Public Data Lecture notes by Austin Troy, University of Vermont © Using GIS--

Fundamentals of GIS GIS Data Acronyms! USGS National Map ©2009 Austin Troy

Fundamentals of GIS ©2009 Austin Troy DLG Digital Line Graphs; U.S. Geological Survey (USGS) Derived from either aerial photographs or from manual and automated digitizing methods. Digital representations of planimetric information: points, lines and areas Full range of attribute codes, full topological structuring, have passed quality-control.

Fundamentals of GIS ©2009 Austin Troy DLG Summary

Fundamentals of GIS ©2009 Austin Troy Transportation layerHypsography and Public land boundary layers

Fundamentals of GIS ©2009 Austin Troy DLG Users Guides DLG Standards documentation available at Download, user guides, abstracts and metadata available for each DLG product at : earthexplorer.usgs.gov earthexplorer.usgs.gov Three DLG layers: hypsography, vegetation cover and roads

Fundamentals of GIS ©2009 Austin Troy DLG Category and Attribute Coding Attributes come in coded form in PAT tables To know what these codes signify, see web page 3/3dlg0798.pdf 3/3dlg0798.pdf Example: Vegetation Cover Layer, Item “Identity_lab” in PAT Outside area Woods or brushwood Scrub Orchard or plantation Vineyard Scattered trees Void area

Fundamentals of GIS ©2009 Austin Troy DLG-Medium Scale Example

Fundamentals of GIS ©2009 Austin Troy DLG-Small Scale Example

Fundamentals of GIS ©2009 Austin Troy DLG Availability Go to This shows hypsography coverage at 1:24000

Fundamentals of GIS ©2009 Austin Troy DLG Availability This shows vegetative coverage at 1:24000

Fundamentals of GIS ©2009 Austin Troy Digital Elevation Models Raster-based data structure for storing terrain data Stores regular array of points in space with spot elevation values Available for free from USGS, EROS Data Center Continuous coverage of lower 48, Hawaii and limited portions of Alaska Made from vector hypsography and hydrography data Still used by some, but no longer maintained by USGS

Fundamentals of GIS ©2009 Austin Troy National Elevation Dataset (NED) New-generation Digital Elevation model; is a complement, not a replacement to DEM They are seamless (not tiled); can be downloaded as a single scene for a large area Avoids terrain errors/discontinuities at border of tiles Filtering process yields fewer “artifacts” and errors; improves quality of terrain analyses and hydro modeling

Fundamentals of GIS ©2009 Austin Troy NED Here is an example of errors generated in drainage channel interpolation with an old DEM vs a NED

Fundamentals of GIS ©2009 Austin Troy NED Referenced to NAD83 Downloaded from seamless server as Arc Grid files Comes in one arc-second pixel size (~30 meters) for entire US Comes in 1/3 arc second (~10 meters) pixel size for much of the US too In a small number of areas is in 1/9 arc second (~3 meters) Status maps available at

Fundamentals of GIS ©2009 Austin Troy NED 10 and 30 meter coverage: from Seamless.usgs.gov

Fundamentals of GIS ©2009 Austin Troy NED Download: rectangle-defined areas as seamless tiles from along with many other data types

Fundamentals of GIS ©2009 Austin Troy NED NED homepage : NED is free for FTP downloads of under 10 megabytes Larger areas either have to be downloaded separately, or purchased as a bulk order.

Fundamentals of GIS ©2009 Austin Troy NED For large areas, can purchase pre-defined zones on CD/DVD

Fundamentals of GIS Shuttle Radar Topography Mission (SRTM) Space Shuttle Endeavor, February 2000 International project (NASA, NGA…) The most uniform (nearly) global elevation dataset 30m resolution for US; 90m for the world Useful complement to older NED data ©2009 Austin Troy

Fundamentals of GIS National Land Cover Dataset (NLCD) ©2009 Austin Troy

Fundamentals of GIS National Land Cover Dataset (NLCD) ©2009 Austin Troy Available for 1992 and category land cover classification scheme based on 1992 Landsat data Comes in image format 30 meter square spatial resolution Available for free from

Fundamentals of GIS ©2009 Austin Troy NLCD classes are somewhat different from 1992 and are not designed to be compared for many class types. E.g. “developed-open space”; many areas classed as low density urban in 1992 Hence change analysis not recommended; however a retrofit of NLCD 1992 was done to allow comparison NLCD 2006 is in progress as NLCD moves from being a mapping program to a monitoring program

Fundamentals of GIS NLCD 1992 and 2001 classification schemes ©2009 Austin Troy Descriptions at

Fundamentals of GIS ©2009 Austin Troy NLCD 2001 Also includes layers of percent canopy cover and percent imperviousness. These can be downloaded or viewed through a viewer online at imperviousness canopy

Fundamentals of GIS ©2009 Austin Troy NLCD:accuracy Improved accuracy in 2001 Accuracy tables for 1992 by region available at accuracy tables still under development 1992 regions (EPA regions) 2001 regions/ reference points

Fundamentals of GIS NLCD accuracy: 1992 ©2009 Austin Troy

Fundamentals of GIS NOAA Coastal Change Analysis Program (C-CAP) Standardized, regional land cover 30m resolution (like NLCD) Began in mid 1990s Goal: update every 5 years 85% accuracy standard ©2009 Austin Troy

Fundamentals of GIS ©2009 Austin Troy DOQs Digital orthophoto quarter quadrangle Also known as DOQQ Old version is scanned photos, from the National Aerial Photography Program (NAPP) One-fourth of a 7.5-minute USGS topographic map 1 meter spatial resolution

Fundamentals of GIS ©2009 Austin Troy Digital Orthophoto Quadrangles Comes in three extents: 3.75 minute quarter quad (140 megs for color) 7.5 minute quad: limited availability, 140 megs for BW Seamless DOQs from

Fundamentals of GIS ©2009 Austin Troy The difference between an aerial photograph and an orthophoto Aerial photo –image displacement caused by tilting of camera and terrain relief –scale is not uniform –cannot measure distances on a photograph Orthophoto –rectified to remove non- constant scale due to varying distance to camera –Also adjusts for elevation and tilt –Therefore possible to measure distances directly like on other maps –Can serve as a base map onto which other info may be overlaid Light travels longer distance at scene edge: magnification

Fundamentals of GIS ©2009 Austin Troy DOQ Documentation Download, metadata and user guides available at Standards Documentation available at

Fundamentals of GIS ©2009 Austin Troy Scanned image of a U.S. Geological Survey (USGS) standard series topographic map The image inside the map neatline is georeferenced to the surface of the earth and fit to the Universal Transverse Mercator projection. The map is scanned at a minimum resolution of 250 dots per inch Digital Raster Graphics (DRG)

Fundamentals of GIS ©2009 Austin Troy Used on-screen to collect, review, and revise other digital data, especially digital line graphs, DLG. DRG’s are available at and at some state GIS repositories have them too for freewww.gisdatadepot.comwww.mapmart.com Digital Raster Graphics (DRG)

Fundamentals of GIS ©2009 Austin Troy This database contains information about almost 2 million physical and cultural geographic features in the United States. The Federally recognized name of each feature described in the data base is identified, and references are made to a feature's location by State, county, and geographic coordinates. Point coordinates are given in latitude/longitude Often abstracts large features to a point USGS Geographic Names Information System (GNIS)

Fundamentals of GIS ©2009 Austin Troy Includes location, names and category of features such as: Schools/universities Churches/cemeteries Airports/ports Parks/recreation centers Shopping centers Stadiums/arenas Theaters/auditoriums/cultural facilities Country clubs/golf courses Marinas/yacht clubs Trailheads (some) Rural fire stations (some) Dams/reservoirs Cities/incorporated areas (as points) GNIS

Fundamentals of GIS ©2009 Austin Troy Information, downloads and a query engine available at: Files export as zipped text file. Can be imported into Excel The query engine can tell you the following about any named geographic feature you input: Latitude/longitude Elevation Estimated 1994 population of cities Feature type GNIS