DEMs, LULC

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DEMs, LULC Soil data

• INLS 110-111
• GIS Digital Information
• Uses, Resources Software Tools

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DEMs Digital Elevation Models

• Raster model digital data
• Federal Agency Dept of Interior
• US Geological Survey (USGS) National Mapping
  Division
• Widespread format scales available correspond
  to DLGs

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DEM Background

• Consist of sampled array of elevs. for a number
  of ground positions at regularly spaced
  intervals.
• Composed of integer values in grid form
  topographic map hypsography overlay
• Available in 7.5-minute, 15-minute, 2-arc-second
  (also known as 30-minute), and 1-degree units.

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DEM Usage

• Used for generating graphics
• isometric projections displaying slope, direction
  of slope (aspect), terrain profiles between
  designated points.
• Also combined with other data types
• stream location data and weather data to assist
  in forest fire control
• with remote sensing data to aid in the
  classification of vegetation.

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DEM Applications

• Modeling terrain gravity data for use in locating
  energy resources
• Determining the volume of proposed reservoirs
• Calculating the amount of material removed during
  strip mining
• determining landslide probability
• developing parameters for hydrologic models

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DEMs Creation

• Some created by scanning National High Altitude
  Photography (Level-1)
• Others derived from DLG data or photographs
  incorporating
• elements from hypsography
• (contours, spot elevations)
• elements from hydrography
• (lakes, shorelines, drainage) (Level 2 3)
• Beware projections datum's vary

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USGS -United States Geological Survey

• Produces 5 primary types of elevation data
• 1 degree DEM (SMALL SCALE)
• ( 3 x 3 arc second spacing)
• 2 arc second/30 min DEM (MEDIUM SCALE)
• (2 x 2 arc second spacing)
• 7.5 minute DEM (LARGE SCALE)
• (30 x 30 meter spacing)
• 7.5 min Alaska DEM
• (1 x 2 arc second spacing)
• 15 minute Alaska DEM
• (2 x 3 arc second spacing)

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DEMs Three Classification Levels

• Level-1
• elevation data sets in standardized format
• Intended for 7.5 min DEMs (large scale)
• Created by scanning NHAP
• Accuracy vertical RMSE of 7 meters desired, 15
  meters max. permitted

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DEMs Three Classification Levels

• Level-2
• elevation data sets processed or smoothed for
  consistency edited to remove errors.
• Derived from hypsographic hydrographic
  digitizing
• Accuracy a RMSE of one-half the contour interval
  is max. permitted.

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DEMs Three Classification Levels

• Level-3
• data sets derived from DLG hypsography
  hydrography data incorporates selected elements
  from both
• Accuracy a RMSE of one-third of the contour
  interval is max. permitted.

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DEM RESOLUTION

• defined as separation between elevation points on
  horizontal grid
• elevation points equally spaced
• Two common ways to specify separation
• meters used in Universal Transverse Mercator
  (UTM) grids when linear measurements specify
  distance
• arc seconds used in geographic coordinate
  grids when angular measurements specify distance

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DEMs Available

• Large Scale
• Spacing 30 x 30 meter UTM projection for each
  7.5 x 7.5 min block also 15 x 15 minute units
  163,360.
• Correspond to USGS 124,000 and 125,000 scale
  topographic quadrangle map series for US its
  territories.
• Alaska 7.5-minute DEM data correspond to the same
  scales, but unit sizes vary depending on the
  latitudinal location of the unit. Projection
  coordinate systems also differ.

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DEM 124,000 30 meter format
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DEMs Available

• Intermediate Scale
• Spacing 30 x 30 minute areas (2-arc-second)
• Correspond to east or west half of USGS 30 x 60
  minute (1100,000) topographic quadrangle map
  series for the conterminous US Hawaii.
• Each 2-arc-second unit is produced and
  distributed as four 15 x 15-minute cells. The
  spacing of elevations along and between each
  profile is 2 arc seconds.

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DEMs Available

• Small Scale
• Spacing 1 x 1 degree blocks (3 x 3 arc-second
  spacing)
• Coverage available for contiguous US, Hawaii, and
  most of Alaska.
• 10 DEMs referred to as 3-arc-second or 1250,000
  scale DEM data.
• Basic elevation model produced by or for the DMA
  (Defense Mapping Agency), but distributed by USGS
  in DEM data record format. In reformatting the
  product, USGS doesnt change basic elevation
  information.

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DEM 1250,000 3-arc format
Image Source Clarke, Keith C. (2001). 3rd Ed.
Getting Started with Geographic Information
Systems. p 95. Fig. 3.18.
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DEM Image shaded to show topography
Scranton, PA East 1250,000 DEM.
Image Source Clarke, Keith C. (2001). 3rd Ed.
Getting Started with Geographic Information
Systems. p 95. Fig. 3.18.
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Raster Graphic DEM Examples
Large Scale Sturgis, SD DEM (7.5 minute)
Jewel Cave Nat'l Monument, SD
Intermediate Scale Sheridan, Wyoming DEM (30
minute)
Small Scale Yellowstone DEM (1 degree block)
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DEM Data Organization

• DEM files organized into three logical records
• Type A contains information defining DEM
  characteristics, including name, boundaries,
  units of measurement, min./max. elevations,
  projection parameters, number of type B
  records.
• Type B contains profiles of elevation data
  associated header information.
• Type C contains statistics on the accuracy of
  the data.

for record examples http//edc.usgs.gov/glis/hype
r/guide/usgs_dem7m12
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National Elevation Dataset (NED)

• Seamless data
• based on 1 arc second spacing most of US 2 arc
  for Alaska
• variety of elevation units, horizontal datums,
  projections
• uses geographic coordinates NAD 83 horizontal
  NAVD 88 vertical datum

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North American Digital Elevation Model- ESRI
derived from the global DEMGTOPO30 data sets
from the U.S. Geological Survey's EROS Data
Center Distributed Active Archive Center (EDC
DAAC)
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North American Shaded Relief - ESRI

• derived from the global DEMGTOPO30 data sets
  from the U.S. Geological Survey's EDC DAAC

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Shaded relief generated from raster elevation
data portrays the land surface. Shown combined
with the topographic map content from the USGS
digital raster graphic of Juneau, Alaska.
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LULC - Land Use Land Cover

• Vector model Raster Models of digital data
• Federal Agency Dept of Interior
• US Geological Survey (USGS) National Mapping
  Division
• Widespread format primary scale 1250,000
• All LULC data conform to the Universal Transverse
  Mercator (UTM) projection.

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LULC Content

• Files describe
• vegetation, water, natural surface, and cultural
  features on the land surface.
• Uses Anderson Classification System
• The USGS provides these data as part of its
  National Mapping Program.
• LULC mapping program designed to compliment
  standard topographic maps (scales of 1250,000
  some cases1100,000)

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LULC Creation

• Manual interpretation of aerial photographs from
  NASA high-altitude missions other sources
• Secondary sources from earlier land use maps
  field surveys also used (as needed)
• Later digitized to create a national digital LULC
  database. (resulting GIRAS)
• National Land Cover Dataset

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LULC Vector Image
Image Sourcehttp//edcwww.cr.usgs.gov/glis/graphi
cs/guide/1_250_lulc/figure1.gif
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2 Formats Vector (GIRAS) or Raster (CTG)

• Available for most of the contiguous US Hawaii
• Distributed in the GIRAS or CTG formats through
  anonymous FTP (for free)
• FTP files are available sorted by state
• 1250,000-scale sorted by state
• 1100,000-scale sorted by state

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VECTOR Geographic Information Retrieval
Analysis System (GIRAS)

• Fixed length records (ASCII) each may consist of
  1 to 16 data-element fields.
• Each data-element field may be one of 3 types
• 16 bit binary integer
• 32 bit binary integer or
• a string of text characters.
• file structure map header, section header, arc
  records subfile, coordinate subfile, polygon
  records subfile, file of arcs by polygon (FAP)
  subfile, text subfile and an associated data
  subfile.
• Topological Vector Model

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RASTER Composite Theme Grid (CTG)

• Files are sequential and consist of fixed length
  records (except for header files)
• One grid cell for each logical record.
• Grid cells contain point sample of the quad where
  the center point of each cell is 200 meters apart
  from other center points in adjacent cells.
• cells mapped to the UTM projection

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LULC Applications

• Compatible w/variety of USGS other data
• Example socioeconomic data compiled by the
  Bureau of Census can be compared to LULC data
• Frequently used in conjunction with DLG and DEM
  data to assist in
• river basin planning, barrier island change
  analysis, environmental impact statement
  preparation urban development studies.

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LULC Examples

• LULC Gwynns Falls Watershed, Baltimore Cty, MD
• Upper Susquehanna-Lakawanna Watershed

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Other Popular Data types

• Soil Data for GIS - Overview
• STATSGO State Soil Geographic Database
• SSURGO Soil Survey Geographic Database