Openstreetmap-carto: Render emergency=siren

[1ec5]

Outdoor warning sirens (emergency=siren) are relevant to public safety and are useful for pedestrian orientation (such as in a park), so it would be great if they would show up at a high zoom level. They tend to be more prominent than power=poles (rendered at z16+) but less prominent than, say, man_made=water_towers (z17+). They’re even more prominent when actively sounding. 🙉

Sirens are sometimes mounted on rooftops, such as fire station roofs, which raises the possibility of collisions. But if we restrict them to z18+, then there would be fewer collision issues. Maybe location=roof sirens could be filtered out, relegated to higher zoom levels, or given lower precedence than other POI icons, but I don’t know how feasible these approaches would be.

(I was sure I saw an issue about sirens in the past, but GitHub insists there’s no issue in this repository regarding sirens yet. Apologies if it’s a duplicate.)

[jeisenbe]

I downloaded the 4596 sirens in the database mapped as ways or nodes. All but 14 are mapped as nodes, and the wiki suggests that this is the recommended mapping method. This is relevant: the key emergency=* is not imported as a polygon feature when mapped as a closed way, but this isn't a problem for a rendering based on a node only.

About 350 currently render due to other tags on the same node, mainly man_made=tower and man_made=mast (since most free-standing sirens will be supported by a pole or tower), and a little over 400 have location=roof or =rooftop and might be excluded from rendering, based on how we render other man_made features.

Over half (2705) of the mapped sirens are in Germany; you can roughly see the borders of Germany in these nodes alone. However, there are still 1885 in the rest of the world, which suggests it might be a frequent enough feature to consider.

It may be difficult to find a intuitive rendering; this would be the most challenging step.

[Prince-Kassad]

I am not convinced yet that this is a suitable feature to render on a general-purpose map.

[jeisenbe]

@1ec5 the wiki page Tag:emergency=siren now suggests that man_made=mast + tower:type=siren be added to free-standing sirens on a tall mast or pole.

If this advice is followed these features will be rendered without adding a new rule.

In theory we could have a subtle difference in the man_made=mast icon when combined with tower:type=siren, but I believe we already have too many different tower and mast type icons.

Thoughts?

[1ec5]

I just added that after seeing the same suggestion at the tower:type=siren page. Seems like this combination has been used in an import in Europe, though none of the editors currently facilitate it. The icon that results isn’t very intuitive, but it does cover freestanding sirens, as opposed to the rooftop sirens that seem likely to collide out more important POI icons.

[jeisenbe]

Do you have a rendering suggestion?