Introduction to GIS

Lecture 16:Public Data 1: USGS Data Sources

Lecture notes by Austin Troy, University of Vermont © 2008

------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

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DLG SummaryProduct

Corresponds to: Available layers

7.5-minute by 7.5-minute Large Scale DLGs

USGS 7.5 minute 1:20,000-,1:24,000-, 1:25,000-scale topographic quadrangle

Hypsography, hydrography, surface cover, non-vegetative features, boundaries, survey markers, transportation; manmade features, and Public Land Survey System

30-minute by 30-minute Intermediate Scale DLGs

half of a USGS 30- by 60-minute 1:100,000 scale topographic quadrangle

Public Land Survey System, boundaries, transportation, hydrography and hypsography

Small scale national atlas sectionals

USGS 1:2 million-scale sectional maps of the National Atlas of the United States of America

boundaries, transportation and hydrography

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Transportation layer Hypsography and Public land boundary layers

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DLG Users Guides

DLG Standards documentation available at http://rockyweb.cr.usgs.gov/nmpstds/dlgstds.htmlDownload, user guides, abstracts and metadata available for each DLG product at : http://earthexplorer.usgs.gov

Three DLG layers: hypsography, vegetation cover and roads

Introduction to GIS

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DLG Category and Attribute Coding• Attributes come in coded for in PAT tables• To know what these codes signify, see web page

http://rockyweb.cr.usgs.gov/nmpstds/acrodocs/dlg-3/3dlg0798.pdf

• Example: Vegetation Cover Layer, Item “Identity_lab” in PAT

• 000 0000 Outside area• 070 0101 Woods or brushwood• 070 0102 Scrub• 070 0103 Orchard or plantation• 070 0104 Vineyard• 070 0105 Scattered trees• 070 0106 Void area

Introduction to GIS

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DLG-Medium Scale Example

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DLG-Small Scale Example

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DLG Availability• Go to http://statgraph.cr.usgs.gov/viewer.htm

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

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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

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• 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

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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.

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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

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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

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NED

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•NED allows you to download rectangle-defined areas as seamless tiles in their browser at http://seamless.usgs.gov, along with many other data types (described later)

Introduction to GIS

©2008 Austin Troy

NED

10 and 30 meter coverage: from Seamless.usgs.gov

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NED• 1/3 arc second NED (about 3 m)

©2008 Austin Troy

Introduction to GIS

NED

©2008 Austin Troy

•NED homepage : http://edc.usgs.gov/products/elevation/ned.html

•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: http://ned.usgs.gov/Ned/historic.asp

Introduction to GIS

©2008 Austin Troy

NED• For large areas, can purchase pre-defined

zones on CD/DVD at http://ned.usgs.gov/Ned/index.asp

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National Land 1992 Cover Data

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•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 http://edc.usgs.gov/products/landcover/nlcd.html or at

http://seamless.usgs.gov

http://gisdata.usgs.net/website/MRLC/viewer.php

•Land cover type codes given at http://landcover.usgs.gov/classes.asp

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National Land Cover Data

• Available for 1992 and 2001

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NLCD 1992 and 2001 classification schemes

©2008 Austin Troy

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NLCD:accuracy•Improved accuracy in 2001

•Accuracy tables for 1992 by region available at http://www.epa.gov/mrlc/accuracy.html

•2001 accuracy tables still under development

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1992 regions (EPA regions)2001 regions/ reference points

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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

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NLCD accuracy: 1992

©2008 Austin Troy

• This is the one for New England: level 2

Back to Top

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NLCD 2001• Also includes layers of percent canopy cover and

percent imperviousness. • These can be downloaded or viewed through a

viewer online at http://gisdata.usgs.net/website/MRLC/viewer.php

imperviousness canopy

Introduction to GIS

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NLCD 2001

• 2001 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

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Digital Orthophoto QuadranglesComes 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 http://seamless.usgs.gov

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 athttp://edcsns17.cr.usgs.gov/EarthExplorer/

Standards Documentation available at

http://rockyweb.cr.usgs.gov/nmpstds/doqstds.html

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

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Used on-screen to collect, review, and revise other digital data, especially digital line graphs, DLG.

DRG’s are available at www.gisdatadepot.com and at www.mapmart.com; some state GIS repositories have them too for free

Introduction to GIS

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•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)

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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)

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GNIS

Introduction to GIS

©2008 Austin Troy

Information, downloads and a query engine available at: http://geonames.usgs.gov

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