PI-7-4 
DCW, WBDb-II and satellite classified information. 
Fig-2 Existing streamlines in DCW data set 
and they are difficult to detect. 
(2) The automated extracted river systems in flat area 
have artificial controlled direction. 
(3) Some watersheds have no outlet to ocean such as 
rivers in Tibetan Plateau. These closed watersheds can 
not be defined by using only DEM. 
So there are some but serious differences between 
computer extracted streamlines and reliable 
streamlines described in Atlas or existing data sets, and 
they are difficult to detect and correct by manual work. 
An algorithm introduced below makes consistent 
DDM and streamlines using reliable data sets such as 
a) An integrated water body/non water body mask 
image (Data-A) is prepared using USGS Land Cover 
Data, DCW streamlines and WBDb-II streamlines. 
By using USGS Land Cover Data, the connectivity of 
streamline data of DCW and WBDb-II is improved 
and the computer extracted stream line can have some 
spread of water body like lake and wide rivers. 
b) Inland isolated river basins are picked up. 
c) Buffer area (Area-A) of 5 pixels buffer distance 
from WBDb-II streamline data is created. 
The existing streamlines in DCW and WBDb-II are not 
always laid on lines extracted by computer. There is 
inconsistency between existing streamlines and 
topographic information derived from DEM. By using 
buffering technique, adequate streamline position is 
defined. 
d) Drainage directions(flow directions) of pixels in 
Area-A is defined. All pixels in Area-A which has 
Fig-3 Computer extracted streamlines with relief shading image