[WIP] Render salt ponds.

[StyXman]

Fixes #545.

Changes proposed in this pull request:

• Render salt ponds with a flat old pink color. This reflects the fact that salt ponds tend to be colorful. Also the white salt dots recently introduced could be added.

Test rendering with links to the example places:

https://www.openstreetmap.org/way/694107134

Before

After

This is closely related to #3901.

[jeisenbe]

The location shown for testing may not be ideal, because there seems to be overlap between the wetland=saltmarsh and landuse=salt_pond areas.

The pink/purple color is somewhat similar to industrial and commercial areas. While salt ponds have some similarities to quarries and industry, we had discussed trying a shade of blue, since these features are intermittently covered with water, and adding a pattern in addition, in #545.

Perhaps we could try the triangular pattern that @imagico has used in his map style? See https://github.com/imagico/osm-carto-alternative-colors/blob/alternative-colors/symbols/patterns/salt_pond.svg and https://github.com/imagico/osm-carto-alternative-colors/blob/alternative-colors/symbols/patterns/salt_pond.png

[imagico]

Generally a good idea but the color does not work for me either.

[StyXman]

The location shown for testing may not be ideal, because there seems to be overlap between the wetland=saltmarsh and landuse=salt_pond areas.

So I'm looking for freestanding salt_ponds?

[StyXman]

I'm going to have an issue here:

https://www.openstreetmap.org/way/108543652#map=14/47.4039/-2.4703

As you can see, the salt_pond contains a lot of basins. Whatever we choose here, it's going to be on top of everything else, like the pink blobs in the sshot above.

[jeisenbe]

https://www.openstreetmap.org/way/108543652 is not mapped according to the usual way that is documented at Tag:landuse=salt_pond - only the (intermittent) water areas should get this tag. Fortunately, most of the salt ponds in your screenshot are mapped correctly - all those east of Kercabellec have the tag landuse=salt_pond just on each pond, e.g. https://www.openstreetmap.org/way/142063430 and https://www.openstreetmap.org/way/142063459 - and rendering these similar to other water areas should help give feedback in support of consistent mapping.

[jeisenbe]

Whatever we choose here, it's going to be on top of everything else, like the pink blobs in the shot above.

That's only true if we render landuse=salt_pond with priority over natural=water. While I think that is the correct option, you could also render areas as water if double-tagged with landuse=salt_pond + natural=water - this is very common. In that case, we would need to use a pattern, like salt_pond.png, rendered on top of water areas, so that the landuse is still visible.

[jeisenbe]

Example with ocean-color and salt_pond.png pattern for landuse=salt_pond:

Next to the facebook offices, in East Palo Alto:

• Unfortunately, there is an overlapping natural=wetland area, perhaps because the landuse=salt_pond doesn't render, though the geometry is different.
• Note also that the wetland overlaps the coastline on the north side.
  https://www.openstreetmap.org/relation/7352305#map=15/37.4903/-122.1583
  

Salt ponds in South Australia:

• These are also tagged with natural=water
  https://www.openstreetmap.org/#map=14/-34.8186/138.5977
  z13 after
  

z14 after

[jeisenbe]

@StyXman what do you think about the option with the pattern
shown in #3905 (comment) ?

[pnorman]

I don't think the pink works because it is too similar to industrial.

[jeisenbe]

This needs rebasing for v5.0.0 - should I do this myself and take over this PR so that @StyXman gets credit for starting this, or would it be clearer I close this PR and open a new one with the designs in #3905 (comment) ?

[pnorman]

This needs rebasing for v5.0.0 - should I do this myself and take over this PR so that @StyXman gets credit for starting this, or would it be clearer I close this PR and open a new one with the designs in #3905 (comment) ?

Do a new PR because you're not going to be reusing any of the commits here

[StyXman]

@jeisenbe thanks for thinking in terms of credit. I don't care much about it, really. Currently I have no time to work on these :(