Title: DEMs, LULC
1DEMs, LULC Soil data
- INLS 110-111
- GIS Digital Information
- Uses, Resources Software Tools
2DEMs 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
3DEM 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.
4DEM 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.
5DEM 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
6DEMs 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
7USGS -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)
8DEMs 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
9DEMs 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.
10DEMs 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.
11DEM 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
12DEMs 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.
13DEM 124,000 30 meter format
14DEMs 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.
15DEMs 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.
16DEM 1250,000 3-arc format
Image Source Clarke, Keith C. (2001). 3rd Ed.
Getting Started with Geographic Information
Systems. p 95. Fig. 3.18.
17DEM 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.
18Raster 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)
19DEM 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
20National 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
21North 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)
22North American Shaded Relief - ESRI
- derived from the global DEMGTOPO30 data sets
from the U.S. Geological Survey's EDC DAAC
23Shaded 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.
24LULC - 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.
25LULC 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)
26LULC 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
27LULC Vector Image
Image Sourcehttp//edcwww.cr.usgs.gov/glis/graphi
cs/guide/1_250_lulc/figure1.gif
282 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
29VECTOR 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
30RASTER 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
31LULC 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.
32LULC Examples
- LULC Gwynns Falls Watershed, Baltimore Cty, MD
- Upper Susquehanna-Lakawanna Watershed
33Other Popular Data types
- Soil Data for GIS - Overview
- STATSGO State Soil Geographic Database
- SSURGO Soil Survey Geographic Database