the web page of Thanh NGO-DUC | TRIP2 / Flow Direction Map

Flow direction map
River sequence map
Elevation map
Extract a region of interest
Mask the upstream region of one given point

In this version of TRIP 2, we provide the 1.0 degree and 0.5 degree global flow direction map.

You can build a flow direction map with different resolution and for different regions by yourself. Some "rules" for the flow direction map that you should follow are listed below:

Each grid point is allocated a number which indicates the outflow direction from the grid point. Grid point can have eight outflow directions; North (1), North East (2), East (3), South East (4), South (5), South West (6), West (7), and North West (8).

8	1	2
7	9	3
6	5	4

Missing value is -9999.
"9" implies that no outlet from that grid point. It could be a river mouth or an inland depression.
Example with the 1.0 degree global flow direction map

[thanh@shui 1.0_deg_global]$ ncdump -h 1.0_deg_flwdir.nc

netcdf 1.0_deg_flwdir {

dimensions:

lon = 360 ;

at = 180 ;

variables:

float lon(lon) ;

lon:units = "degrees_east" ;
lon:valid_min = -180.f ;
lon:valid_max = 180.f ;
lon:long_name = "Longitude" ;

float lat(lat) ;

lat:units = "degrees_north" ;
lat:valid_min = -90.f ;
lat:valid_max = 90.f ;
lat:long_name = "Latitude" ;

int flwdir(lat, lon) ;

flwdir:missing_value = -9999 ;

}

Note: In the flow direction map, the longitude values were saved from "small to big". The latitude values were saved from "big to small".