[OSM-talk] Mapping rivers that flow into/through lakes?

Christoph Hormann osm at imagico.de
Thu Feb 22 23:02:34 UTC 2018

On Thursday 22 February 2018, Rory McCann wrote:
> What's the best way to map rivers that flow into lakes, especially
> when another river flows through it? Should they be connected?
> [...]

This has been discussed in the past occasionally and IIRC there was 
never full agreement on the matter.  A few things that are important to 

* The question if a river flows through a lake or if it enters a lake 
and ends there is not generally something that can be answered 
* In well mapped areas where a lake has one large outflow and only one 
or a few similarily large inflows they are often connected.
* In most cases with larger lakes smaller inflows are not connected.
* In contrast to riverbank polygons where there is in principle a well 
established rule where to place the waterway (the thalweg) there is no 
established rule how rivers that are connected within a lake are to be 
placed or connected.
* There is also no established rule if waterways within a lake get the 
name and other tags from the tributaries they connect or if they are to 
be without name tag.  Both variants are common.
* The vast majority of waterbody imports import without connectivity, 
even if connected data is available like in the US and Canada.

Part of the problem is of course that the task of generating waterway 
connectivity within a water area or supplementing an incomplete 
connectivity are cumbersome mechanical tasks.  So the ultimate question 
probably is if this is something editors should provide support to 
produce automatically or if it is something that data users should 
generate automatically as needed.

Christoph Hormann

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