Convert a lake in a river

[MarinoBuia]

How to do that?

here

thx

[Flash]

You don't, a lake is a POI (with the polygon option used) and a river is a line feature.

[Flash]

Also, this sure looks like a River that was damned to make a lake.  I think calling the feature a lake is correct.  Since it is a man made lake in the middle of a river, which does continue on either end, you could also draw a river down the middle of it, that would not visually show since they are the same colour but the river name would then appear on the reserviour at regular intervals.

[MarinoBuia]

It is a lake hundreds of km  long , it is difficult to decide where it begins as lake

[MarinoBuia]

here the dam

[MapperCE]

Draw "water"-shapes, but don't remove the river - adjust it if it's outside the water.

[tosommerfugle]

Does that mean that you suggest that rivers should generally always be mapped continously as such from beginning to end, through lakes which can fairly be called wide river segments?

[Flash]

No, that's a different situation.  When major rivers a damned like this, they are still considered to be a river, with a reservoir portion.  That reservoir usually gets a name along the line of "<dam name> Lake", but it is still technically a river with a slack water portion.  Natural rivers and lakes, however, are normally designated as one or the other and named as such.  I don't know of any rivers that empty into a lake, and then the river that drains the lake has the same name.  Do you have an example of one?

[tosommerfugle]

Rivers having the same name before and after lakes are a normal thing in Denmark, especially for modestly-sized natural lakes having only one significant inlet. The country is small, so our major rivers are also small, but this map of Gudenå (bold blue line) shows what I'm referring to. Several natural lakes near the center of the image. A bit further towards the top is Tange Sø, which is named just like any other lake, but is technically a slack water reservoir for a historical hydroelectric power plant. It would be "nice" to have a continuous route for the river, as it has one clear identity all the way, and is popular for canoing.

Another example is currently a mess on Google Maps. The marker is near a series of "elongated lakes" (without connection), where the broader part of each ends at a historical watermill. The river name "Mølleåen" is used from the larger lake to the west (Furesø) before and after the lake Lyngby Sø (natural and "enhanced" with a dam) from which Mølleåen is meandering to the north and east. I'm considering if the river should be mapped continuously, at least from Lyngby Sø to the coast, but leave the lakes (wide river segments) as they mark where there is water.

[Flash]

Interesting to know, I love how Map Maker teaches about other parts of the world.  My best advice then would be to go with the official naming.  So if the governement and perhaps geography departments at universities consider the river to be cotinuous, even as it pass through the lake, then I would map it as such and quote those sources (making sure you are not linking to any copyrighted sources).  If, however, you find that governement and scholars say that the river is just where the water is free flowing, then that is probably how it should be mapped.

I'm not saying this is the absolute directives on the situation, but rather what makes logical sense.  Research it, map it, give the evidence, and see what the reviewers say.