Pl-7-2 
products with reliable products are required, however 
it will be difficult if the data size become huge. 
In this paper, global DDM excluding Antarctica are 
produced using GTOPO30 - global 30 second arc 
DEM provided by USGS and some other global data 
sets. A similar products are now available as “HYDRO 
IK, Elevation Derivative Database” at USGS, which 
includes data sets of (1) Aspect , (2) Flow 
Directions ,(3) Flow Accumulations (4) Slope (5) 
Compound Topographic Index. The URL of the site 
is: 
http://edcwww.cr.usgs.gov/landdaac/gtopo30/hydro/in 
dex.html 
However the available data of “HYDRO-IK” are only 
two - North America and Africa - and other continents 
- South America, Asia, Europe and Australia - are still 
under the processing( October 1998). Furthermore, the 
algorithm and the accuracy of river network systems 
are not clear in “HYDRO-IK” at this moment. This 
paper describes the detail of the developed algorithm 
for DDM generation and reliability of the extracted 
river systems. 
2. USED DATA 
The used data to generate the global DDM are as 
follows: 
GTOPO30 
30 seconds arc Digital Elevation Model of the world 
lands, provided by USGS. 
The accuracy of the data is not equally qualified 
because the data sources are varied. GTOPO30 is one 
of the precise mesh elevation data covering the entire 
world land area. The data is also available at following 
site, and detail of the data can be obtained. 
http://edcwww.cr.usgs.gov/landdaac/gtopo30/ 
gtopo30.html 
DCW River Data 
Digital Chart of the World (DCW) includes the world 
river system(stream line) data as “DNNET” coverage 
in LINE feature. Because the data is ARC/Info format, 
it is converted to 30 seconds grid raster format. 
WBDb-II River Data 
World Boundary Databank -II is data sets provided by 
U.S. Department of State(DoS)/ Central Intelligence 
Agency(CIA), and it includes the global river system 
data. Because the data is ARC/Info format, it is 
converted to 30 seconds grid raster format. The data 
density is no so high as DCW river data, and it means 
that river systems in WBDb-II data set are more 
significant river systems than DCW river systems. The 
location of river lines are not exactly same as DCW’s 
river lines. The data can be obtained from UN/GRID. 
USGS 1km Land Cover. 
The data is provided by USGS. It is classified image 
using 1km 10 days composite data from April 1992 to 
March 1993 combined with other global data sets such 
as GTOPO30 and existing vegetation maps. There are 
6 maps provided based on 6 category systems such as 
1. Global Ecosystem Legend, 2. IGBP Land Cover 
Legend, 3. USGS Land Use/Land Cover System 
Legend, 4. Simple Biosphere Model Legend, 5. Simple 
Biosphere 2 Model Legend , 6. Biosphere Atmosphere 
Transfer Scheme Legend. In this paper, ”3. USGS 
Land Use/Land Cover System Lend” is used to get 
information of “water body” distribution which is not 
described in DCW nor WBDb-II data sets. The data 
can be obtained from following URL: 
http://edcwww.cr.usgs.gov/landdaac/glcc/glcc. 
html