Distinguish artifical water features from (semi)-natural water

jeisenbe commented 3 years ago

Expected behavior

Provide mappers feedback by distinguishing (semi)natural water areas from artificial reservoirs, canals, ditches,

Actual behavior

Streams appear similar to ditches and drains, rivers are similar to canals
All water areas are the same color and lack an outline.
Mappers have no feedback about missing water=reservoir and water=basin tags on artificial lakes, and landuse=reservoir / landuse=basin are not distinguished from natural=water lakes.

Possible solutions

Add a lighter centerline for artificial waterway lines
Add a darker outline for artificial water areas (reservoirs, canal areas etc): this would need to be done along with using a darker color for rivers to look right. For canals it would be difficult without pre-processing
Subtle regular pattern for artificial water areas?

imagico commented 3 years ago

For waterway=stream/river vs. ditch/drain/canal i agree. See also #2346, #3354.

For artificial water areas - i am afraid the difference in meaning between the different tags is not very well defined for standing water (i.e. water=lake vs. water=reservoir)

Lake Victoria for example is tagged as water=lake:

https://www.openstreetmap.org/relation/2606941

despite being artificially level regulated and used for hydropower generation.

The Schluchsee OTOH:

https://www.openstreetmap.org/relation/1651189

is tagged as a reservoir. This is a perfectly valid choice of tagging but it is not documented how the line is drawn between a water level regulated lake and a reservoir and i am not sure if there is consensus about this in the mapper community.

In general i think solving #4128, #3895 and #3468 should have precedence over this.

jeisenbe commented 3 years ago

Re: Lake Victoria for example is tagged as water=lake: https://www.openstreetmap.org/relation/2606941 despite being artificially level regulated and used for hydropower generation.

I was not aware that Lake Victoria had a dam near it’s outlet. It’s worth noting that the dam does not appear to have been intended to increase the lack level, though 5 years after it’s construction the lake level unexpectedly rose due to heavy rainfal and after that, the operators chose to maintain the lake level about 1 to 1.5 meters higher than historical averages. However, it’s fair to say that over 90% of the lake surface was natural, and the current lake level and surface area is within the natural range of variation: https://web.archive.org/web/20060109075544/http://www.fas.usda.gov/pecad/highlights/2005/09/uganda_26sep2005/

So there seems to be nothing surprising about considering Lake Victoria a natural lake

In contrast The Schluchsee https://www.openstreetmap.org/relation/1651189 had a much smaller natural lake at this location, and the great majority of the current water area is created by the large dam: https://en.wikipedia.org/wiki/Schluchsee#/media/File:Schluchsee-Ursee.jpg - so it seems like mappers are choosing to call this a reservoir since most of the lake level and area is due to the dam.

In general i think solving #4128, #3895 and #3468 should have precedence over this.

I agree. This would be “nice to have” if it were easy enough to do, but certainly not the priority.

gravitystorm / openstreetmap-carto