Transcript Accessing and Using Public Data

------Using GIS-Fundamentals of GIS
Lecture 16:
Data Input I: Selected Public Data
Lecture notes by Austin Troy, University of Vermont © 2008
Fundamentals of GIS
GIS Data
• Acronyms!
• USGS National Map
©2009 Austin Troy
Fundamentals of GIS
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
©2009 Austin Troy
Fundamentals of GIS
DLG Summary
Product
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
30-minute by
30-minute
Intermediate
Scale DLGs
Small scale
national
atlas sectionals
half of a USGS 30- by 60minute 1:100,000 scale
topographic quadrangle
Hypsography, hydrography,
surface cover, non-vegetative
features, boundaries, survey
markers, transportation;
manmade features, and
Public Land Survey System
Public Land Survey System,
boundaries, transportation,
hydrography and
hypsography
USGS 1:2 million-scale
sectional maps of the
National Atlas of the
United States of America
©2009 Austin Troy
boundaries, transportation
and hydrography
Fundamentals of GIS
Transportation layer
Hypsography and Public
land boundary layers
©2009 Austin Troy
Fundamentals of GIS
DLG Users Guides
DLG Standards documentation available at
http://nationalmap.gov/standards/dlgstds.html
Download, user guides, abstracts and metadata available for
each DLG product at :
http://eros.usgs.gov/#/Find_Data/Products_and_Data_Av
ailable/DLGs
Three DLG layers:
hypsography, vegetation cover
and roads
©2009 Austin Troy
Fundamentals of GIS
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
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000 0000
070 0101
070 0102
070 0103
070 0104
070 0105
070 0106
Outside area
Woods or brushwood
Scrub
Orchard or plantation
Vineyard
Scattered trees
Void area
©2009 Austin Troy
Fundamentals of GIS
DLG-Medium Scale Example
©2009 Austin Troy
Fundamentals of GIS
DLG-Small Scale Example
©2009 Austin Troy
Fundamentals of GIS
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
©2009 Austin Troy
Fundamentals of GIS
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
©2009 Austin Troy
Fundamentals of GIS
NED
•Here is an example of errors generated in drainage
channel interpolation with an old DEM vs a NED
©2009 Austin Troy
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
NED
10 and 30 meter coverage: from Seamless.usgs.gov
©2009 Austin Troy
Fundamentals of GIS
NED
• Download: rectangle-defined areas as seamless tiles from
http://seamless.usgs.gov, along with many other data types
©2009 Austin Troy
Fundamentals of GIS
NED
• Free for FTP download (size limit!)
• For large areas, can purchase pre-defined zones on
CD/DVD
©2009 Austin Troy
Fundamentals of GIS
Shuttle Radar Topography Mission (SRTM)
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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)
• 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 from
http://seamless.usgs.gov
http://gisdata.usgs.net/website/MRLC/viewer.php
Lecture notes by Austin Troy©009
& Brian
Voigt,
University of Vermont © 2011
Austin
Troy
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
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
1992 regions (EPA regions)
2001 regions/ reference points
©2009 Austin Troy
Fundamentals of GIS
NLCD accuracy: 1992
©2009 Austin Troy
http://landcover.usgs.gov/accuracy/
Fundamentals of GIS
NOAA Coastal Change Analysis Program (C-CAP)
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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
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
©2009 Austin Troy
Fundamentals of GIS
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
http://seamless.usgs.gov
©2009 Austin Troy
Fundamentals of GIS
The difference between an aerial photograph
and an orthophoto
• Aerial photo
• Orthophoto
– image displacement caused
by tilting of camera and
terrain relief
– scale is not uniform
– cannot measure distances
on a photograph
Light travels
longer distance at
scene edge:
magnification
©2009 Austin Troy
– rectified to remove nonconstant 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
Fundamentals of GIS
DOQ Documentation
Download, metadata and user guides available at
http://online.wr.usgs.gov/ngpo/doq/
Standards Documentation available at
http://nationalmap.gov/standards/doqstds.html
©2009 Austin Troy
Fundamentals of GIS
Digital Raster Graphics (DRG)
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
©2009 Austin Troy
Fundamentals of GIS
Digital Raster Graphics (DRG)
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
©2009 Austin Troy
Fundamentals of GIS
USGS Geographic Names
Information System (GNIS)
• 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
©2009 Austin Troy
Fundamentals of GIS
GNIS
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)
©2009 Austin Troy
Fundamentals of GIS
GNIS
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
©2009 Austin Troy