Proposal:Intermittently Exposed Lakebed and Riverbed
| Intermittently Exposed Lakebed and Riverbed | |
|---|---|
| Proposal status: | Draft (under way) |
| Proposed by: | Harahu |
| Applies to: | 
|
| Definition: | Areas that alternate between being covered by rivers or lakes and being exposed to the air. |
| Rendered as: | 
|
| Draft started: | 2022-12-09 |
Proposal
As of December 2022 the last remaining areas tagged waterway=riverbank, but not natural=*, has been converted to a more modern river area schema (natural=water + water=river). We are left in a situation where waterway=riverbank is used for a single remaining purpose; the mapping of intermittent river areas, where one also cares about mapping what is exposed when the intermittent river is not covering the area. This usage accounts for approximately 1300 river areas, exclusively in Norway. It is not a straightforward task to upgrade these remaining areas, as the natural=* tag is already in use to describe the riverbed of the area. Whether or not to upgrade these areas, and how, has caused controversy in the Norwegian mapping community.
Given these low usage numbers, it is reasonable to assume that the support for the waterway=riverbank in rendering engines might be dropped, like has already happened in editors like iD and JOSM, or left unimplemented.Therefore it is desirable to transition to a new schema, based on the modern schema (natural=water + water=river), such that rendering of these areas are preserved for the future. This proposal is an attempt at defining what this new tagging schema should look like.
Independently, it has become evident to the author that a similar issue exists for areas intermittently covered by standing water. The most common example of this phenomena are reservoirs. Since it would be desirable to have a single method for mapping both riverbed and lakebed, the proposal aims at covering both of these cases.
Rationale
There are two fundamentally different ways one could go about mapping rivers with riverbed. I refer to these methods as "single area" and "superimposed areas". The first class tries to gather the tags for both the river area and the riverbed on the same area. The second treats the river and the riverbed as distinct objects by using distinct polygons for either.
The method currently used in Norway is an instance of the "single area" strategy. One could imagine replacing this schema either with a new "single area" schema, or the more radical "superimposed areas" idea.
Tags currently describing riverbed surface:
surface=* riverbed:riverbank=* riverbed:riverbottom=* riverbed=* riverbed:type=*
| Class | Tagging style | Consistent with modern river area mapping | Correctly rendered in Carto today | Adheres to | Concept extendable to standing water | Required mapping effort | Discoverability though Overpass API |
|---|---|---|---|---|---|---|---|
| Single area | waterway=riverbank
natural=* |
❌ | ✅ | ❌
(Treats river and riverbed as the same object) |
❌
(natural tag taken) |
✅ Low | ✅ wr["waterway"="riverbank"]["intermittent"="yes"]["natural"];
out body;
>;
out skel qt;
|
| natural=water
water=* riverbed=* OR riverbed:natural=* OR natural:riverbed=* (OR any other dedicated key to describe riverbed surface) |
✅ | ❌ | ❌
(Treats river and riverbed as the same object) |
❌
(Implies subdividing lakes or reservoirs, leading to problems with rendering the name of the reservoir) |
✅ Low | ✅wr["natural"="water"]["intermittent"="yes"]["riverbed"];
out body;
>;
out skel qt;
| |
| Superimposed areas | Area 1 (river)
water=*
natural=* |
✅ | ✅ | ✅ | ✅ | ⚠️ Higher
(requires n + 1 areas instead of n, where n is the number of distinct riverbed areas per river section) |
⚠️ No appropriate query found for this one yet...
https://community.openstreetmap.org/t/discovering-riverbed-and-lakebed-areas-using-overpass-how/6865 |
Tagging
Examples
Rendering
Having a method for mapping riverbed and lakebed allows us to go from a simple rendering, like this:
... to something more nuanced, like this:
Features/Pages affected
External discussions
Discussions predating proposal
Waterway=riverbank only left in Norway
Comments
Please comment on the discussion page.