1. Digital Data Sources Chapter 7
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2. 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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3. 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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4. Map Services vs Locally Stored
Some data is available for transfer to, storage on, and manipulation in a local computer.
Other data are available as a Web service.
Web Mapping Service (WMS) – this is the most common form
Web Coverage Service (WCS)
Web Feature Service (WFS)
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5. Web Mapping Service
A Web Map Service (WMS) is a standard protocol for serving (over the Internet) georeferenced map images which a map server generates using data from a GIS database.
The Open Geospatial Consortium developed the specification and first published it in 1999.
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6. Web Coverage Service
A WCS provides access to coverage data in forms that are useful for client-side rendering, as input into scientific models, and for other clients.
WCS format encodings allow to deliver coverages in various data formats, such as GML, GeoTIFF, HDF-EOS, CF-netCDF or NITF.
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7. Web Feature Service
In computing, the Open Geospatial Consortium Web Feature Service Interface Standard (WFS) provides an interface allowing requests for geographical features across the web using platform-independent calls.
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8. Advantages & Disadvantages of WMS
They save space on the local drive, but can be slow to respond.
A community of users can share the same data.
Many different kinds of data may be joined.
Often limits the users ability to edit the data.
Some types of analyses may not be supported.
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9. National & Global Digital Data
Global data sets are not commonly available.
Frequently collected around a theme
Collected from satellite imagery, which limits what can be collected.
A few exist:
MODIS – global vegetation canopy
Center for International Earth Science.
Global Land Cover Facility.
ciesin – Columbia
Land Cover – Un. Maryland
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10. Global Spatial Data Infrastructure (GSDI)
An initiative to coordinate collection and processing methods worldwide to ensure that spatial data are broadly suitable for global-level analysis.
Global Map is an early GSDI initiative, specifying 8 thematic layers: boundaries, elevation, land cover, vegetation, transportation, population centers and drainage.
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11. Open Street Map
A GSDI initiative, an open access, user generated resource.
Individuals can check out data sources to modify.
Open Street Map
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12. Digital Data for the U.S.
National Spatial Data Infrastructure (NSDI) defines the policies, technologies, and personnel required to ensure the efficient sharing and use of spatial data.
NSDI has identified framework data commonly used by organizations.
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13. Existing GIS Data Framework Data
Geodetic control – accurately measured positions
Imagery
Geometrically corrected
aerial photos
Satellite imagery
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14. Existing GIS Data
3. Elevation – contour lines and digital elevation models (DEM)
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15. Existing GIS Data Transportation – streets, railroads, ferry lines
Hydrography – focuses on the measurement of physical characteristics of waters and marginal land - lakes, rivers, streams
Governmental units – countries, states/provinces, cities/towns, census blocks, school units, hospital units, etc.
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16. Existing GIS Data
7. Cadastral information
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17. Availability of Framework Data
The National Map
Csv – comma separated values
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18. The National Map May be downloaded as: A shapefile
FileGDB 10.1 (open source)
The FileGDB driver provides read and write access to File Geodatabases (.gdb directories) created by ArcGIS 10 and above.
The dataset name must be the directory/folder name, and it must end with the .gdb extension.
Some of the files are data files which down load as .csv files.
Easily imported into Excel.
Excel worksheets are compatible with ArcGIS.
Csv – comma separated values
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19. The National Map NLCD – National Land Cover Data
10-year repeat cycle, 1991, 2001, 2011
21 landcover classes, based on satellite images, 30 meter cell size
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20. Lecture 7

21. Lecture 7

22. National Land Cover Database
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23. Digital Raster Graphics
The National Map
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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24. Digital Raster Graphic
Source:
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25. Digital Line Graphs (DLG)
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
Obtaining DLG from USGS.
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26. Digital Line Graph
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27. Digital Line Graphs
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
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28. Digital Line Graphs Data is often edge matched along map seams
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)
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29. Data is often edge matched along map seams
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30. 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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31. 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 layers
Vegetation data layers
Time series analysis (temporal changes such as urban expansion)
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33. 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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34. 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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35. 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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36. Cowardian Classification
National Wetlands Inventory (NWI)
Cowardian Classification
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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37. National Wetlands Inventory (NWI)
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38. National Wetlands Inventory (NWI) Cowardian Classification Lecture 7
Palustrine –marsh or swamp
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39. Cowardian Classification --- Lacustrine
National Wetlands Inventory (NWI)
Cowardian Classification Lacustrine
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40. Digital Soils Data National State Level
Natural Resource Conservation Service (NRCS)
(Digital soil data sets at different scales and extents)
National Soil Geography (NATSGO), national coverage, small scale.
State Level
State 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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41. 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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42. Source: http://tahoe.usgs.gov/soil.html
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43. Source: http://tahoe.usgs.gov/soil.html
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44. Digital Soils Data – Accessing Attributes
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45. Digital Elevation Models (DEM)
Raster data sets of elevation
Usually developed using photogrammetric surveys
Useful for slope, aspect, visibility calculations
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46. 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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47. 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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48. Digital Elevation Models
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49. DEM Raster Grid Cells contain elevation values Streams show valley
locations
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50. On maps,
elevation
often depicted
as contour
lines
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51. 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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52. Downloadable Satellite Imagery
Fifteen Free Satellite Imagery Data:
Landsat level 1 data as well as Surface Reflectance and other higher level products:
How to download Landsat 8 imagery:
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53. The Landsat Series
“When Landsat 5 fell silent on 6 January, scientists across the globe mourned its passing but gave thanks for its fortitude. The satellite had lasted a record-breaking 28 years, snapping images of the changing planet from melting glaciers to burning rainforests, while its successors faltered. Landsat 6 failed during launch and Landsat 7, at 13 years old, is partially blind and has limited fuel. With the passing of Landsat 5, the future of the world’s longest-running — and perhaps most influential — set of data on global change rests with Landsat 8, which is scheduled to launch next week from Vandenberg Air Force Base in California.”
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54. Images from the Landsat satellite series show the Aral Sea in central Asia shrinking significantly from 1977 to 2010 because of water diversion for agricultural use
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55. Diversion of water has also shrunk the Dead Sea, where water levels have dropped about 30 meters in the past 50 years. From 1972 to 2011, the southern portion of the sea has been converted into evaporation ponds for extracting minerals.
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56. Between 1986 and 2011, the terminus of the Columbia Glacier in southeastern Alaska retreated by 20 kilometers. Icebergs that broke off the glacier's edge can be seen floating south of the terminus.
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57. How to download free satellite imagery for free.
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58. X,Y Data on the Web
Copy an paste into an Excel 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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59. Data Available from ESRI
From Within ArcMap
Base Maps
These are from a web mapping service and require an internet connection for them to be drawn.
They cannot be or saved to your own computer or edited.
ArcGIS Online
More information than you can imagine.
Some may be saved to your own computer and edited.
Data Files on CD – may be saved and edited
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60. Sources of Free GIS Data
Maine Office of GIS
Idaho Geospatial Office
MassGIS
Data.gov
USGS
U.S. Census Bureau
National Park Service
Wikipedia
Topologically Integrated Geographic Encoding and Referencing system
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