Transcript Introduction to GIS - University of Vermont

------Using GIS-Introduction to GIS
Lecture 16:
Public Data 1: USGS Data Sources
Lecture notes by Austin Troy, University of Vermont © 2008
Introduction to GIS
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 qualitycontrol.
©2008 Austin Troy
Introduction to 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
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boundaries, transportation
and hydrography
Introduction to GIS
Transportation layer
Hypsography and Public
land boundary layers
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Introduction to GIS
DLG Users Guides
DLG Standards documentation available at
http://rockyweb.cr.usgs.gov/nmpstds/dlgstds.html
Download, user guides, abstracts and metadata
available for each DLG product at :
http://earthexplorer.usgs.gov
Three DLG layers:
hypsography, vegetation cover
and roads
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Introduction to GIS
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/dlg3/3dlg0798.pdf
• Example: Vegetation Cover Layer, Item “Identity_lab”
in PAT
•
•
•
•
•
•
•
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
©2008 Austin Troy
Introduction to GIS
DLG-Medium Scale Example
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Introduction to GIS
DLG-Small Scale Example
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Introduction to GIS
DLG Availability
• Go to http://statgraph.cr.usgs.gov/viewer.htm
This shows hypsography coverage at 1:24000
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Introduction to GIS
DLG Availability
This shows vegetative coverage at 1:24000
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Introduction to GIS
DLG Layer Availability in CA-1:24,000
Many layers have
only minimal
coverage at the
1:24000 scale
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Introduction to 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
©2008 Austin Troy
Introduction to GIS
New Elevation Data Set is NED
•The National Elevation Dataset is the newgeneration 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.
©2008 Austin Troy
Introduction to GIS
NED
•Here is an example of errors generated in drainage
channel interpolation with an old DEM vs a NED
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Introduction to GIS
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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Introduction to GIS
NED
•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)
©2008 Austin Troy
Introduction to GIS
NED
10 and 30 meter coverage: from Seamless.usgs.gov
©2008 Austin Troy
Introduction to GIS
NED
• 1/3 arc second NED (about 3 m)
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Introduction to GIS
NED
•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
©2008 Austin Troy
Introduction to GIS
NED
• For large areas, can purchase pre-defined
zones on CD/DVD at
http://ned.usgs.gov/Ned/index.asp
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Introduction to GIS
National Land 1992 Cover Data
•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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Introduction to GIS
National Land Cover Data
• Available for
1992 and
2001
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Introduction to GIS
NLCD 1992 and 2001 classification schemes
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Introduction to 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
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Introduction to GIS
NLCD accuracy: 1992
• 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
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Introduction to GIS
NLCD accuracy: 1992
• This is the
one for
New
England:
level 2
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Introduction to GIS
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
canopy
imperviousness
©2008 Austin Troy
Introduction to GIS
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
©2008 Austin Troy
Introduction to 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
©2008 Austin Troy
Introduction to 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
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Introduction to 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
©2008 Austin Troy
– rectified to remove nonconstant 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
Introduction to GIS
DOQ Documentation
Download, metadata and user guides available
at
http://edcsns17.cr.usgs.gov/EarthExplorer/
Standards Documentation available at
http://rockyweb.cr.usgs.gov/nmpstds/doqstds.html
©2008 Austin Troy
Introduction to GIS
Digital Raster Graphics
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
©2008 Austin Troy
Introduction to GIS
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
©2008 Austin Troy
Introduction to 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
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Introduction to 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)
©2008 Austin Troy
Introduction to 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 1994 population of cities
•Feature type
©2008 Austin Troy