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It seems that during one of the last map updates a small error has crept in. In the map of Switzerland, only the border is visible for part of Lake Zurich, but the blue fill has been lost .
I am also surprised that some partly large lakes in Switzerland are not shown. What is the selection criterion for the lake areas, their size or a special OSM type? Compared to Poland, where some small lakes are visualized, several important lakes are missing in Switzerland.
in Bug reports by smellfooth (4.6k points)

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Lakes are colored blue depending on the maps size (in square-units) and the size of the connected water bodies. Water bodies with these tags are used:

  • lake
  • basin
  • river
  • pond
  • canal
The whole procedure is fairly complex and we played around with different values quite a lot. But basically the water bodies with the above tags are first joined together, then looked at, to see if they are large enough compare to the mapped area.
It's very hard to find values that looks good in all countries at the same time. While some countries might wish more water bodies were added, others might look to cluttered.
by magma1447 (Admin) (235k points)
selected by smellfooth
Thanks a lot for your response. Unfortunately it doesnt explain, why the southern part of Lake Z├╝rich isn't colored. On the map only the boundary is of the lake is visible.

Check this image, to get an impression:
That seems like some form of bug. If it's a data error in OSM or what it is I can't tell right now.

The water-body-data we use was rendered in April this year. I can look into making a new water-extract to see what happens. But the processing of data alone is around 8 hours.