Introduction to GIS Lecture 16: Public Data 1: USGS Data Sources Lecture notes by Austin Troy, University of Vermont © Using GIS--

Introduction to GIS ©2008 Austin Troy DLG Digital Line Graphs; made by the U.S. Geological Survey's (USGS) Derived from either aerial photographs or from manual and automated digitizing methods. They are digital representations of planimetric information that use points, lines and areas Data contain a full range of attribute codes, have full topological structuring, and have passed quality- control.

Introduction to GIS ©2008 Austin Troy DLG Summary

Introduction to GIS ©2008 Austin Troy Transportation layerHypsography and Public land boundary layers

Introduction to GIS ©2008 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

Introduction to GIS ©2008 Austin Troy DLG Category and Attribute Coding Attributes come in coded for 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

Introduction to GIS ©2008 Austin Troy DLG-Medium Scale Example

Introduction to GIS ©2008 Austin Troy DLG-Small Scale Example

Introduction to GIS ©2008 Austin Troy DLG Availability Go to This shows hypsography coverage at 1:24000

Introduction to GIS ©2008 Austin Troy DLG Availability This shows vegetative coverage at 1:24000

Introduction to GIS ©2008 Austin Troy DLG Layer Availability in CA-1:24,000 Many layers have only minimal coverage at the 1:24000 scale

Introduction to GIS Digital Elevation Models ©2008 Austin Troy 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48, Hawaii and limited portions of Alaska Made from vector hypsography and hydrography data Still used by some, but no longer maintained by USGS

Introduction to GIS New Elevation Data Set is NED ©2008 Austin Troy The National Elevation Dataset is the new- generation Digital Elevation model, although it is a complement, not a replacement They are seamless, which means they are not tiled, they don’t generate terrain errors or discontinuities at the border of tiles and that they can be downloaded as a single scene for a large area Their filtering process yields fewer “artifacts” which improves quality of slopes and allows for better modeling of drainage and hydrology.

Introduction to GIS NED ©2008 Austin Troy Here is an example of errors generated in drainage channel interpolation with an old DEM vs a NED

Introduction to GIS ©2008 Austin Troy NED Comes in one arc-second pixel size (~30 meters) for entire US Comes in 1/3 arc second (~10 meters) pixel size for portions of the US, including VT In a few rare places have 1/9 arc second too (VA, WVA, WA) Referenced to NAD83 Downloaded from seamless server as ArcGrid files

Introduction to GIS NED ©2008 Austin Troy NED allows you to download rectangle-defined areas as seamless tiles in their browser at along with many other data types (described later)

Introduction to GIS ©2008 Austin Troy NED 10 and 30 meter coverage: from Seamless.usgs.gov

Introduction to GIS NED 1/3 arc second NED (about 3 m) ©2008 Austin Troy

Introduction to GIS NED ©2008 Austin Troy 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. Some historic NEDs are available:

Introduction to GIS ©2008 Austin Troy NED For large areas, can purchase pre-defined zones on CD/DVD at

Introduction to GIS National Land 1992 Cover Data ©2008 Austin Troy This is is a 21-category land cover classification scheme based on 1992 Landsat data Comes in image format 30 meter square spatial resolution Available for free from or at Land cover type codes given at

Introduction to GIS National Land Cover Data Available for 1992 and 2001 ©2008 Austin Troy

Introduction to GIS NLCD 1992 and 2001 classification schemes ©2008 Austin Troy

Introduction to GIS ©2008 Austin Troy NLCD:accuracy Improved accuracy in 2001 Accuracy tables for 1992 by region available at accuracy tables still under development Introduction to GIS 1992 regions (EPA regions) 2001 regions/ reference points

Introduction to GIS NLCD accuracy: 1992 ©2008 Austin Troy If you click on a region it takes you to a table for two levels of class aggregation This is the one for New England: level 1 Back to Top

Introduction to GIS NLCD accuracy: 1992 ©2008 Austin Troy This is the one for New England: level 2 Back to Top

Introduction to GIS ©2008 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

Introduction to GIS ©2008 Austin Troy NLCD classes are somewhat different from 1992 and are not designed to be compared for many class types. For instance, new classes not in 1992, like “developed-open space”; many areas classed as low density urban in 1992 would be this class in the 2001 map Hence change analysis no recommended; however later 1992 will be reclassed to allow this comparison NLCD 2006 is under plans as NLCD moves from being a mapping to a monitoring program

Introduction to GIS ©2008 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

Introduction to GIS ©2008 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

Introduction to GIS ©2008 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 –adjusts for parallax (change in relative position due to viewing angle) and tilt –also deals with effect of tilt and relief –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

Introduction to GIS ©2008 Austin Troy DOQ Documentation Download, metadata and user guides available at Standards Documentation available at

Introduction to GIS ©2008 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

Introduction to GIS ©2008 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

Introduction to GIS ©2008 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)

Introduction to GIS ©2008 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) Introduction to GIS GNIS

Introduction to GIS ©2008 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