Fundamentals of GIS

Lecture 8:Selected Public Data

Lecture notes by Austin Troy, University of Vermont © 2008

------Using GIS--

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Part 1

US Geological Survey Data Sources

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DLG• Digital Line Graphs; 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.

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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

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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

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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

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DLG Availability

This shows vegetative coverage at 1:24000

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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

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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 and that they

•Filtering process yields fewer “artifacts;” improves quality of slopes and hydro modeling

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NED•Here is an example of errors generated in drainage channel interpolation with an old DEM vs a NED

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NED

• Referenced to NAD83• Downloaded from seamless server as ArcGrid files• Comes in one arc-second pixel size (~30 meters) for

entire US• Comes in 1/3 arc second (~10 meters) pixel size for

much of the US too• In a small number of areas is in 1/9 arc second (~3

meters)• Status maps available at

http://gisdata.usgs.net/website/usgs_gn_ned_dsi/viewer.htm

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NED

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

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

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NED

•NED homepage : http://ned.usgs.gov

•NED is free for FTP downloads of under 10 megabytes

•Larger areas either have to be downloaded separately, or purchased as a bulk order.

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NED• For large areas, can purchase pre-defined

zones on CD/DVD

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National Land Cover Data

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National Land Cover Data

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•Available for 1992 and 2001

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

•Comes in image format

•30 meter square spatial resolution

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

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

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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 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

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NLCD 1992 and 2001 classification schemes

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

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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

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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 development1992 regions (EPA regions)

2001 regions/ reference points

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NLCD accuracy: 1992

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

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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

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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

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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

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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

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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

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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)

GNIS

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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

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Part 2

Data from Other Sources

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• Comes from both the USGS and the EPA• Surface water features: lakes, ponds, streams,

rivers, springs• Nationally consistent• Order of linkages coded to allow for flow path

analysis• Background info at

http://nhd.usgs.gov/techref.html• Resolutions from 1:100k to 1:24k

National Hydrography Dataset (NHD)

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NHD• Many analysis tools designed for this data. For

instance: can find the path upstream or downstream from any point using NHD data and network analyst; flow reaches are numbered sequentially in order of flow to allow path analysis

• Stream reaches encoded like addresses on a street• Connections encoded using topology• Other tools available at http://nhd.usgs.gov/tools.html

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NHD• Download at

http://nhdgeo.usgs.gov/viewer.htm

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NHD

• Can extract by County/state.

• Click on radio button of geography for clip

• Use check marks to make layers visible in base map

• Then Click on clip boundary (e.g. Chittenden County) in the map viewer

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NHD

• Can then choose the resolution and the database type

• Must turn popup blocker off to use

• Then get an email for custom download

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NHD• Contents of

Geodatabase: many feature classes with different purposes

• Many will often be empty

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USDA Data

• USDA houses a number of data layers at their new Geospatial data gateway

• http://datagateway.nrcs.usda.gov/

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USDA Gateway Includes• CLU farm boundaries (not any longer, but SAL has

it for VT))• Hydrologic Units (8 and 12 digit)• NED elevation• Digital Raster Graphics• High resolution color orthophotos from 2003, 2004,

2006 (National Agriculatural Imagery Program)• Geographic Names• Cropland data layer (for some areas)• NRCS Soils data and soils tables• Climate Data (precipitation and temp)

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USDA Gateway Includes

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USDA Gateway Includes

• Can Define clip regions by state or county

• Can also highlight a layer and get information

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Common Land Units

• Farm field boundaries representing smallest contiguous unit of cultivated land

• For farms in USDA programs

• Much more accurate that “agriculture” category in NLCD land cover

• Type of crop is unknown

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NAIP

• National Agricultural Imagery Program

• Digital Imagery, mosaiced by county, used by the NRCS and FSA to look at compliance with subsidy programs

• Ortho-rectified,• Color, 1:40,000 scale• 2003 and 2004

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SSURGO Soils Data• SSURGO: Soil Survey Geographic

Data from NRCS• Soils data also at

http://soildatamart.nrcs.usda.gov/Default.aspx

• Metadata and standards available at http://soildatamart.nrcs.usda.gov/SSURGOMetadata.aspx

• Entails both a polygon layer showing soils area boundaries, but also an Access Database of numerous soil attributes

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SSURGO• Soil Data Mart interface

• Access—sample tables; there are dozens

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USDA Forest Service Data Gateway

• For each National Forest includes layers like: boundaries, trails, roads, ranges for certain tree and animal species, and ecological regions

©2009 Austin Troy

http://svinetfc4.fs.fed.us/vectorgateway

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National Wetlands Inventory• From Fish and Wildlife Service• Maps all class 1 and 2 major wetlands• Available digitally for much of the country• 1:24,000 or smaller• Involves a complex taxonomy of wetlands codes

available at http://www.fws.gov/wetlands/_documents/gNSDI/WetlandsDeepwaterHabitatsClassification.pdf

• Calculator at http://www.fws.gov/wetlands/data/webatx/atx.html

• Includes marine, estuarine, riverine, lacustrine and palustrine types

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NWI• Wetlands map interface at http://wetlandsfws.er.usgs.gov/wtlnds/launch.html

• Allows you to view online data and download

• First shows status availability map:

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NWI• Can make PDFs easily

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NWI

• NWI by wetland type overlaid on NHD streams layer

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Topologically Integrated Geographic Encoding and Reference System

Automates the mapping and related geographic activities required to support the decennial census and sample survey programs of the census bureau starting with the 1990 decennial census.

The Census TIGER® system supports:Creation and maintenance of the digital geographic data base that includes complete coverage of the United States and its territories

TIGER

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The TIGER system provides support for:

• Creation and maintenance of a nation wide digitalgeographic data base

• Production of maps from the TIGER® data base for allCensus Bureau enumeration and publication programs

• Allows for address geocoding

•Can be integrated with Census attribute databases easily

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Accuracy and Attribution:

•TIGER has good attribution, but poor accuracy

•They are based partially on 1:100,000 DLG

•Are often conflated

•This is often used to assign the attributes from TIGER® data to 1:24,000 DLG data

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The TIGER files contain data describing three feature types: •Line Features 1.Roads 2.Railroads 3.Hydrography 4.Transportation and Utility Lines•Boundary Features 1.Statistical boundaries, such as census tracts and blocks 2.Local government boundaries, such as places and counties 3.Administrative boundaries, such as congressional and school districts •Landmark Features 1.Point landmarks, such as schools and churches 2.Area landmarks, such as parks and cemeteries 3.Key geographic locations, such as apartment buildings and factories

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TIGER line files and the demographic filesDirect linkage using keys built up from:

State FIPS code

County FIPS code

Tract number

Block group number

Block number

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For geographic files•ESRI:http://www.esri.com/data/download/census2000_tigerline/index.html

Download 2000 U.S. Census TIGER lines files and demographic data•UC Berkeley Tiger Server:http://sunsite.Berkeley.EDU/GovData/info/tiger.htmlFor attributes to 2000 and 1990 Censushttp://factfinder.census.govFor data in intermediate years via the American Community Surveyhttp://www.census.gov/acs/www/

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Introduction to GIS

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For continuing data updates, check the data links page at http://www.uvm.edu/envnr/gradgis/supplement.html

Here you’ll find links to many state level GIS online data repositories plus many of the ones mentioned here

Another link is to map a network drive to \\zoofiles\gisdata

where you’ll find: NAIP imagery, ortho photos, all VCGI data plus VTrans database, World data from ESRI, DRG topo maps, Street maps USA

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VCGI• The web

site offers many layers through a browser

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• Includes an interactive map browser for “clipping and zipping” data

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Other sources for USGS data• www.mapmart.com

– Allows users to choose tiles and layers with a geographic interface

– Most public data are free, but ,any others available for a price

– Gives status maps

– Can also buy bulk public data for a fee

• www.gisdatadepot.com– Not as user friendly

– Just a plain old interface that is hard to navigate

– However, many free data layers and lots of scripts and extensions