MAP LAYERS

LAYER NAME:

KEHORN

AUTHOR/CREATOR:

USGS/EROS DATA CENTER

ORGANIZATION:

USGS/EROS DATA CENTER

LINK URL:

http://edcdaac.usgs.gov/gtopo30/gtopo30.html

CREATION DATE:

1993

MODIFIED BY:

DATA AND INFORMATION MANAGEMENT UNIT

UNDP_SOMALIA

MODIFICATION DATES:

21/03/2001

ABSTRACT:

The HORN is a clip from the GTOPO30 DEM based on data derived from 8 sources of elevation information including vector and raster data sets. The elevations are regularly spaced at 30-arc seconds (approximately 1 kilometer). The entire data is packed into tiles.

 

CONSTRAINTS:

 

Acknowledgement U.S Geological Survey, the EROS Data Center and UNDP would be appreciated in products derived from these data.

The data should not be used for navigation or for producing maps requiring high geodetic accuracy.

DATASET SIZE (MB):

5.14MB

STATUS

BOUNDING COORDINATES

 EAST:        43.9431                        NORTH:        8.8044

 

WEST:        31.9862                        SOUTH        -5.9274 

POSITIONAL ACCURACY:

The vertical accuracy varies by location according to source data.

± 30 meters linear error by DTED and USGS DEM

±650 meters linear error by DCW data

COORDINATE SYSTEM:

DECIMAL DEGREES

DATUM:

WGS 84

MAP PROJECTION:

GEOGRAPHICAL

FORMAT

GRID format

 

 

TABLES

SOURCE:

USGS/EROS DATA CENTER

SOURCE PUBLICATION DATE:

1993

CONSTRAINTS:

UNKNOWN

DATASET SIZE (MB):

5.14MB

ATTRIBUTE RELIABILITY:

UNKNOWN

STATUS:

COMPLETE

FIELDS:

SEE ATTACHED

 

CONTACT NAME:

Alex Lugadiru

ORGANIZATION:

DEPHA PROJECT

POSTAL ADDRESS:

c/o UNDP DDC

P.O. BOX 30552,

NAIROBI,

KENYA.

EMAIL ADDRESS:

alex.lugadiru@unep.org

TELEPHONE NO.:

254-020-7624186/95
 
GTOPO30 DESCRITION

 

Data for each tile are provided in a set of 8 files. The files are named with the tile name and a file name extension indicating the contents of the with the tile name and a file name extension indicating the contents of the file.  The following extensions are used:
 
Extension         Contents
---------               --------
 DEM      digital elevation model data
 HDR       header file for DEM
 DMW     world file
 STX        statistics file
 PRJ         projection information file
 GIF         shaded relief image
 SRC        source map
 SCH        header file for source map
 
The simple format should allow for easy ingest into most popular image processing and geographic information systems packages.
Further information on the contents of the files is provided below.
 
 
FILES
 
FILE DESCIPTION
 
DEM File (.DEM)
 
The DEM is provided as 16-bit signed integer data in a simple binary raster.
 
 
 
There are no header or trailer bytes imbedded in the image.  The data are
 
 
 
stored in row major order (all the data for row 1, followed by all the data
 
 
 
for row 2, etc.).
 
Header File (.HDR)
 
The DEM header file is an ASCII text file containing size and coordinate
 
 
 
information for the DEM.  The following keywords are used in the header file:
 
 
 
BYTEORDER      byte order in which image pixel values are stored 
 
 
                              M = Motorola byte order (most significant byte first)
 
 
 
LAYOUT             organization of the bands in the file
 
 
 
                             BIL = band interleaved by line (note: the DEM is a single
 
 
 
                             band image)
 
 
 
NROWS              number of rows in the image
 
 
 
NCOLS                number of columns in the image
 
 
 
NBANDS             number of spectral bands in the image (1 for a DEM)
 
 
 
NBITS                  number of bits per pixel (16 for a DEM)
 
 
 
BANDROWBYTES   number of bytes per band per row (twice the number of columns
 
 
 
                              for a 16-bit DEM)
 
 
 
TOTALROWBYTES  total number of bytes of data per row (twice the number of
 
 
 
                             columns for a single band 16-bit DEM)
 
 
 
BANDGAPBYTES   the number of bytes between bands in a BSQ format image
 
 
 
                             (0 for a DEM)
 
 
 
NODATA            value used for masking purposes
 
 
 
ULXMAP            longitude of the center of the upper-left pixel (decimal degrees)
 
 
 
ULYMAP            latitude  of the center of the upper-left pixel (decimal degrees)
 
 
 
XDIM                  x dimension of a pixel in geographic units (decimal degrees)
 
 
 
YDIM                  y dimension of a pixel in geographic units (decimal degrees)
 
World File (.DMW)
 
The world file is an ASCII text file containing coordinate information.  It
 
 
 
is used by some packages for georeferencing of image data.
 
Statistics File (.STX)
 
The statistics file is an ASCII text file which lists the band number,
 
 
 
minimum value, maximum value, mean value, and standard deviation of the
 
 
 
values in the DEM data file.
 
Projection File (.PRJ)
 
The projection information file is an ASCII text file which describes the
 
 
 
projection of the DEM and source map image.
 
Shaded Relief Image (.GIF)
 
A shaded relief image is provided as an overview of the data in each tile.
 
 
 
The images were derived from a generalized version of GTOPO30 with a
 
 
 
horizontal grid spacing of 240-arc seconds (approximately 8 kilometers), so
 
 
 
many small islands and features will not be visible.  The images are meant
 
 
 
to provide a convenient way for users to view the general topographic
 
 
 
features portrayed in each tile.  The shaded relief images are provided as
 
 
 
GIF images which can be displayed by many popular image display programs and
 
 
 
World Wide Web browsers.  An image size of 750 rows by 600 columns is used
 
 
 
for the tiles covering 50 degrees of latitude by 40 degrees of longitude. 
 
 
An image size of 450 rows by 900 columns is used for the Antarctica tiles
 
 
 
which cover 30 degrees of latitude by 60 degrees of longitude each.  The
 
 
 
Antarctica polar stereographic tile is portrayed by a shaded relief image
 
 
 
having 675 rows by 675 columns.
 
Source Map (.SRC)
 
The source map is a simple 8-bit binary image which has values that indicate
 
 
 
the source used to derive the elevation for every cell in the DEM.  The
 
 
 
source map is the same resolution and has the same dimensions and coordinate
 
 
 
system as the DEM.  Like the DEM, it has no header or trailer bytes and is
 
 
 
stored in row major order.  These codes are used in the source map image:
 
 
 
 
 
 
 
Value        Source
 
 
 
-----           ------
 
 
 
  0            Ocean
 
 
 
  1            Digital Terrain Elevation Data
 
 
 
  2            Digital Chart of the World
 
 
 
  3            USGS 1-degree DEM's
 
 
 
  4            Army Map Service 1:1,000,000-scale maps
 
 
 
  5            International Map of the World 1:1,000,000-scale maps
 
 
 
  6            Peru 1:1,000,000-scale map
 
 
 
  7            New Zealand DEM
 
 
 
  8            Antarctic Digital Database
 
Source Map Header File (.SCH)
 
The source map header file is an ASCII text file containing size and coordinate information, similar to the DEM header file. The following keywords are used in the source map header file:
 
 
 
BYTEORDER             byte order in which image pixel values are stored 
 
 
                                    M = Motorola byte order (most significant byte first)
 
 
 
LAYOUT                   organization of the bands in the file
 
 
 
                                    BIL = band interleaved by line (note: the source map is
 
 
 
                                    a single band image)
 
 
 
NROWS                      number of rows in the image
 
 
 
NCOLS                       number of columns in the image
 
 
 
NBANDS                    number of spectral bands in the image (1 for the source map)
 
 
 
NBITS                         number of bits per pixel (8 for the source map)
 
 
 
BANDROWBYTES   number of bytes per band per row (the number of columns for
 
 
 
                                     an 8-bit source map)
 
 
 
TOTALROWBYTES  total number of bytes of data per row (the number of columns
 
 
 
                                     for a single band 8-bit source map)
 
 
 
BANDGAPBYTES     the number of bytes between bands in a BSQ format image
 
 
 
                                     (0 for the source map)
 
 
 
NODATA                     value used for masking purposes
 
 
 
ULXMAP                     longitude of the center of the upper-left pixel (decimal degrees)
 
 
 
ULYMAP                     latitude of the center of the upper-left pixel (decimal degrees)
 
 
 
XDIM                           x dimension of a pixel in geographic units (decimal degrees)
 
 
 
YDIM                           y dimension of a pixel in geographic units (decimal degrees)