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Figure 1 GTOPO30
3.1. GTOPO30
GTOPO30 is a global digital elevation model (DEM) with a
horizontal grid spacing of 30 arc seconds (approximately 1
kilometer). GTOPO30 was derived from several raster and vector
sources of topographic information made through a collaborative
effort led by staff at the US. Geological Survey’s EROS Data
Center (EDC). It is available through the Internet, and GSI also
manages the mirror site in the following URL.
Figure 2 Global Land Cover Characterization
3.2.Global Land Cover Characterization
The U.S. Geological Survey (USGS), the University of Nebraska-
Lincoln (UNL), and the European Commission’s Joint Research
Centre (JRC) have generated a 1-km resolution global land cover
characteristics data base for use in a wide range of environmental
research and modeling applications. The global land cover
characteristics data base has 1-km nominal spatial resolution, and are
based on l-km Advanced Very High Resolution Radiometer
(AVHRR) data spanning April 1992 through March 1993.
3.3. Vector Map Level 0 (Digital Chart of the
World)
Vector Map (VMap) Level 0 is an updated and improved version of
the National Imagery and Mapping Agency's (NIMA) Digital Chart
of the World (DCW). The VMap Level 0 database provides
worldwide coverage of vector-based geospatial data which can be
viewed at 1:1,000,000 scale. It was generated by NIMA with the
from Web page of EROS data center, USGS
http://wwwl1.gsi-mc.go.jp/gtopo30/gtopo30.html
In each month, 400-800 accesses to GSI’s mirror site have been
recorded (as of the end of March 1998).
from Web page of EROS data center, USGS
collaborative effort of the military survey departments of Australia,
Canada and UK.
4. Draft Technical Specifications
4.1. Outline
Draft Technical Specifications prescribe that Global Map is the data
sets which have following characteristics.
e As the data base covers the whole land area of the earth,
ITRF94 coordinate system is adopted as reference coordinate
system. GRS80 ellipsoid is adopted to represent the position
of spatial objects in longitude and latitude.
e Each file covers the divided area consisting of five
degrees in latitude by five degrees in longitude. The point
whose latitude and longitude are zero is a corner of one of
these blocks. Feature instances in each layer located in each
block are stored in a file.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 485
