© RivEX 2017
Your dataset must be a vector dataset
Your vector dataset must be of polyline (arcs) feature type
Polylines must be connected to each other only at their ends (nodes)
Polylines must be digitised in a source (From) to mouth (To) direction
The polyline represents the centre line of the river and not the banks
Lakes and reservoirs should be reduced to centre lines so that a connected network is formed
RivEX will process networks that conform to the following specifications:
A network as seen on a map
The topological network, lakes and rivers have been reduced to centrelines
River networks that RivEX cannot process
River networks can be displayed in a variety of formats. Depending upon scale and symbology a river may appear to be a network which RivEX could process. The following are examples of networks which are not topologically correct vector networks.
Polyline (but not topologically correct)
Many rivers are displayed and analysed in raster format. If your river network has a pixellated appearance as shown in the image below then your data is in raster format and RivEX cannot process this.
Rivers are often captured on maps as polygons, especially wide rivers. If your data is in polygon format then this cannot be processed by RivEX. The images below show a section of river that first appears to be a valid network but when zoomed in it is clearly a polygon and cannot be processed.
Rivers may be captured as lines but the network is not topologically correct. Below is an image of a network that should not be processed by RivEX. The RED circle indicates the point at which a river has exceeded a threshold size and is now being displayed with its left and right bank. Technically this is a network as it is still composed of polylines but the stream ordering algorithm expects a single line to represent the channel not left and right banks. The GREEN circle indicates water bodies, most likely lakes, that are not part of the network. Such polylines should be removed from the dataset.
Section of river which appears to be a single line
Section of river zoomed in clearly shows that it is a polygon