# [Tagging] Using multipolygons to map bays in Alaska

Christoph Hormann osm at imagico.de
Fri Nov 16 13:31:36 UTC 2018

```On Friday 16 November 2018, Daniel Koc4‡ wrote:
>
> It would be much more useful if you tell now how to verify position
> of this node?

Quoting from:

https://wiki.openstreetmap.org/wiki/Tag:natural%3Dstrait

"when mapping as a node this node should usually best be placed
approximately in the middle between the coasts of the strait at the
narrowest point"

And just for ease of everyone the matching quote from

https://wiki.openstreetmap.org/wiki/Tag:natural%3Dbay

"When you map a bay as a node the node should be placed approximately at
the middle of the bay with equal distance to the coast enclosing the
bay on all sides."

In the previous discussion i linked to i formulated it a bit more
precisely:

"If you want to formulate a formal mathematical rule for where the node
for a bay is best placed: Place it so the variance of the distance of
the node to the bay's shores is minimized.  Most existing nodes comply
with this rule remarkably well."

--
Christoph Hormann
http://www.imagico.de/

```