Fundamentals of GIS

Lecture 16:Data Input I: Selected Public Data

Lecture notes by Austin Troy, University of Vermont © 2008

------Using GIS--

Fundamentals of GIS

GIS Data

• Acronyms!

• USGS National Map

©2009 Austin Troy

Fundamentals of GIS

©2009 Austin Troy

Digital Line Graph (DLG)• 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.• More information at http://eros.usgs.gov/#/Guides/dlg

Fundamentals of GIS

©2009 Austin Troy

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

Fundamentals of GIS

©2009 Austin Troy

Transportation layer Hypsography and Public land boundary layers

Fundamentals of GIS

©2009 Austin Troy

DLG Users GuidesDLG Standards documentation available at http://nationalmap.gov/standards/dlgstds.htmlDownload, user guides, abstracts and metadata available for each DLG product at : http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/DLGs

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

http://nationalmap.gov/standards/pdf/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

Fundamentals of GIS

©2009 Austin Troy

DLG-Medium Scale Example

Fundamentals of GIS

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DLG-Small Scale Example

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

NED

• NED homepage: http://ned.usgs.gov

• Available at http://seamless.usgs.gov as raster dataset– One arc-second pixel size (~30 meters) for entire US

– 1/3 arc second (~10 meters) pixels for much of the US

– 1/9 arc second (~3 meters) pixels for a small number of areas

• Status maps @ http://ned.usgs.gov/usgs_gn_ned_dsi/viewer.htm

Lecture notes by Austin Troy & Brian Voigt, University of Vermont © 2011

Fundamentals of GIS

Lecture notes by Austin Troy & Brian Voigt, University of Vermont © 2011

Fundamentals of GIS

©2009 Austin Troy

NED10 and 30 meter coverage: from Seamless.usgs.gov

Fundamentals of GIS

©2009 Austin Troy

NED• Download: rectangle-defined areas as seamless tiles from http://seamless.usgs.gov, along with many other data types

Fundamentals of GIS

©2009 Austin Troy

NED• Free for FTP download (size limit!)• 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

• http://srtm.usgs.gov/

• 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)

©009 Austin Troy

• Available for 1992, 2001, & 2006

• 21-category land cover classification scheme based on 1992 Landsat data

• 20-categories in 2001 & 2006

• 30-meter spatial resolution

• Available free fromhttp://seamless.usgs.gov

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

Lecture notes by Austin Troy & Brian Voigt, University of Vermont © 2011

Fundamentals of GIS

NLCD 2001

• 2001 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 moves from being a mapping program to a monitoring program– 2006 data collection comparable to 2001

Lecture notes by Austin Troy & Brian Voigt, University of Vermont © 2011

Fundamentals of GIS

NLCD Classification Schemes

Descriptions at http://www.epa.gov/mrlc/definitions.html

Lecture notes by Austin Troy & Brian Voigt, University of Vermont © 2011

Fundamentals of GIS

NLCD 2001 & 2006• Includes layers of percent canopy cover and percent

imperviousness.

% imperviousness % canopy

Lecture notes by Austin Troy & Brian Voigt, University of Vermont © 2011

Fundamentals of GIS

©2009 Austin Troy

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 development1992 regions (EPA regions)

2001 regions/ reference points

Fundamentals of GIS

NLCD accuracy: 1992

©2009 Austin Troyhttp://landcover.usgs.gov/accuracy/

Fundamentals of GIS

NOAA Coastal Change Analysis Program (C-CAP)• Standardized, regional land cover (and more!)

• http://www.csc.noaa.gov/crs/lca/ccap.html

• 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 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

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 athttp://online.wr.usgs.gov/ngpo/doq/

Standards Documentation available at http://nationalmap.gov/standards/doqstds.html

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 http://data.geocomm.com/drg/index.html; some state GIS repositories also have them for free

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: 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 city population• Feature type

GNIS