L9 – Digital Data SourcesChapter 7

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Introduction• Data – measurements and observations

• Data quality – a measure of the fitness for use of data for a particular task (Chrisman, 1994).

• Metadata – data about the data– Coordinate system & datum– Extent– Timeliness– Accuracy– Availability for use

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Existing GIS Data

• By U.S. law, any data collected with government money must be made available to the public for free, or cost of reproduction.

• This is NOT true in other countries where the data is viewed as a source of income.

• It is the responsibility of the GIS user to determine the “fitness of use” of the data for his/her purposes.

• Check the metadata!

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Existing GIS Data• Framework Data (7 basic layers)

1. Geodetic control – accurately measured positions

2. Orthoimagery – geometrically corrected aerial photos

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Existing GIS Data• Framework Data (7 basic layers)

3. Elevation – contour lines and digital elevation models (DEM)

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Existing GIS Data• Framework Data (7 basic layers)

4. Transportation – streets, railroads, ferry lines

5. Hydrography – focuses on the measurement of physical characteristics of waters and marginal land - lakes, rivers, streams

6. Governmental units – countries, states/provinces, cities/towns, census blocks, school units, hospital units, etc.

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Existing GIS Data• Framework Data (7 basic layers)

7. Cadastral information

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Identify, Obtain, and Import

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NLCD – National Land Cover Data10-year repeat cycle, 1991, 2001, 2011

21 landcover classes, based on satellite images, 30 meter cell size

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http://www.mrlc.gov/nlcd2011.php

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Digital Raster Graphics•A scanned image of a U.S. Geological Survey (USGS) map

•Georeferenced to the Universal Transverse Mercator projection

•Scanned at a minimum resolution of 250 dots per inch.

•Digital raster graphics (DRG) were produced from 1995 to 1998 by the U.S. Geological Survey (USGS)

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Digital Raster Graphic

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Source:http://mcmcweb.er.usgs.gov/drg/

•A Digital Line Graph (DLG) is a cartographic map feature represented in digital vector form that is distributed by the U.S. Geological Survey (USGS). •DLGs are collected from USGS maps and are distributed in large-, intermediate- and small-scale with up to nine different categories of features, depending on the scale.• Digitized by USGS using standard methods, little accuracy lost in conversion, available at well below their production cost

Digital Line Graphs (DLG)

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 Separate themes provided (4 for 1:100,000, 11 for 1:24,000)

•Boundaries (political & administrative•Hydrography (lakes, rivers, glaciers)•Roads•Hypsography (elevation contours)•Transportation•Vegetation & non Vegetation features (sand, gravel)•Monuments & Control points•Public Land Survey System•Man-made features

Delivered as text or binary files, use conversion utilities to convert to vendor-specific data files

Digital Line Graphs

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Data is often edge matched along map seams(though sometimes one map series has been updated and not the adjoining maps so manual edge matching is required)

Most often in UTM coordinate system

Several formats are provide such as DLG-3 or SDTS (Spatial Data Transfer Standard)

DLG’s provide limited attribute data but conveys important topological and categorical relationships (road type; major/minor road, unpaved)

Digital Line Graphs

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DLG Hydrography DLG Roads

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Digital Line Graph

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http://shannonmapcatalog.blogspot.com/2010_07_01_archive.html

Data is often edge matched

along map seams

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USGS Digital Orthophoto Quadrangles (DOQ)•Orthophotos - corrected for distortions due to camera tilt, terrain displacement, and other factors. •Nationwide availability (nearly)

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USGS Digital Orthophoto Quadrangles (DOQ)

As most features larger than 1 meter are visible these images are the basis of many types of analysis and other data layers, for example:

Establishing ground control points.Creating or updating roads data layersVegetation data layersTime series analysis (temporal changes such as urban expansion)

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National Wetlands Inventory (NWI)

• Data on the location and condition of wetlands throughout much of the United States

• National Inventory, created by the US Fish and Wildlife Service

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National Wetlands Inventory (NWI)

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National Wetlands Inventory (NWI)

Maps depict wetlands as interpreted from photos taken on a single (usually Spring or Summer) date.

Photo-interpreted, surface water and wetland vegetation are keys to identification.

Ephemeral wetlands (e.g., floodplain forests, vernal pools) and those with sub-surface water tables often missed, particularly if vegetation structure similar (e.g., “fresh” meadows).

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National Wetlands Inventory (NWI)

Typical minimum mapping unit (MMU) are between .5 and 2 hectares (vary by vegetation, source, region, etc.)

NWI depict wetland by type with a hierarchical classification scheme with modifiers

Not statutory definition of wetlands.

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National WetlandsInventory (NWI)

CowardianClassification

http://wetlands.fws.gov/Pubs_Reports/Class_Manual/class_titlepg.htmLecture 9 28

National Wetlands Inventory (NWI)

•Systems are Marine, Estuarine, Riverine, Lacustrine (lakes), and Palustrine (marsh/swamps)

•Subsystems subtidal, intertidal, tidal, perennial, intermittent, limnetic (away from shore) and littoral (near shore)

•Class defines general bottom or vegetation conditions (e.g., rock bottom, scrub-shrub wetland).

There are at least two shortened designators which may appear on wetlands maps,

U = Uplands, and OUT = out of the mapped area.

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National WetlandsInventory (NWI)

CowardianClassification

http://wetlands.fws.gov/Pubs_Reports/Class_Manual/class_titlepg.htmLecture 9 30

National Wetlands Inventory (NWI)Cowardian Classification --- Lacustrine

http://wetlands.fws.gov/Pubs_Reports/Class_Manual/class_titlepg.htmLecture 9 31

National Wetlands Inventory (NWI)Cowardian Classification --- Paustrine

http://wetlands.fws.gov/Pubs_Reports/Class_Manual/class_titlepg.htmLecture 9 32

Digital Soils Data

NationalNatural Resource Conservation Service (NRCS)(Digital soil data sets at different scales and extents)

National Soil Geography (NATSGO), national coverage, small scale.

State LevelState Soil Geographic (STATSGO) data intermediate scale and resolution. (1:250,000)

Soil Survey Geographic (SSURGO) data at a very large scale provides the most spatial and categorical detail. (used by land owners, farmers, planners – county level)

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Digital Soils Data

SSURGO data are developed from soil surveys (field and photo measurements)

Soil Surveys are digitized and have positional accuracy similar to the 1:24,000 quad maps. (< 13m for 90% of points)

Extensive detail (other data files) about individual soil series can be linked via a unique identifier. (soil chemistry, physical properties, suitability for building, depth to bedrock,

etc.)

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Source: http://tahoe.usgs.gov/soil.htmlLecture 9 35

Source: http://tahoe.usgs.gov/soil.html Lecture 9 36

Digital Soils Data – Accessing Attributes

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Digital Elevation Models (DEM)

• Raster data sets of elevation

• Usually developed using photogrammetric surveys

• Useful for slope, aspect, visibility calculations

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Digital Elevation Models (DEMs) May be defined as digital representations of earth's surface

Typically point fields in layer (may be raster or vector, note this can't represent overhangs)

•Represent elevation using a raster data model •As with the DLGs they are available from several origins and accuracies.•The most useful for most natural resource applications are based on the 1:24,000 USGS topographic map series

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DEMs produced using any one of several methods:

-Gestalt photomapper, parallax on photopairs

-Interpolated from digitized contours

-Interpolated from points (low relief) Data delivered with a 30-meter grid cell size.

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Digital Elevation Models

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http://lab.visual-logic.com/2010/02/creating-terrain-with-the-displace-modifier/

DEM

RasterGrid

Cells containelevationvalues

Streamsshowvalley locations

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On maps,elevationoften depictedas contourlines

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Only a partial list today. There are also:

• Floodplain data (FEMA)

• Federal managed lands (e.g., USFS, BLM)

• State road networks through DOT

• EPA watershed boundary and river reach data

• and many more

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Map Services vs Local Storage

• Some data is available for download.

• Other is via a WMS (web map services) which eliminates the need for a local copy.– Data is displayed on a local machine but

stored remotely.– The data is delivered as needed when

panning or zooming.– Often this data cannot be manipulated or

changed.

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Sources of Free GIS Data

• Maine Office of GIS• Idaho Geospatial Office• MassGIS• U.S. Census Bureau• National Resource Conservation Service• U.S.G.S.• National Park Service• GIS Data Depot• http://www.diva-gis.org/gdata• http://freegisdata.rtwilson.com/• Wikipedia

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X,Y Data on the Web

• http://volcano.oregonstate.edu/oldroot/volcanoes/alpha.html

• Copy an paste into an Excel (97-03) spreadsheet or a text file.

• Add it to your project as an X,Y Event theme.

• Convert to a shapefile or feature.

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Progress Report

• October 15th

• List of data files and their source.

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