Joseph, I am not sure you will get some response to “...it needs testing...”
especially not from GIS and vector map-makers. To do such analyses one should
start from the source data, should have a robust tool-set and be willing to
invest lot of work and time to compare, measure, run applications and so on. If
the “switching” issue is only a low scale rasterization and display efficiency
related then the whole issue IMO is irrelevant (arguments). However, in GIS and
vector map-making, especially from the scientific point of view, the coastline
land polygons vs. ocean polygons issue is essential. This issue was many times
up to discussion and they were various data versions of these polygons
available, some used in the OSM main map layers.
Some years ago I made a pretty detailed analyses of the coastline large
land/water polygons and their generalized (scale level) versions and published
the results here
https://lists.openstreetmap.org/pipermail/dev/2016-June/029295.html . Last
several days I have invested to repeat some of the work done in the link to see
the present state of the polygons in focus. Many of the mentioned anomalies in
the former article are still there though by reduced extent. Some short related
notes:
-The former polynomial polyline smoothing is replaced with a cartographic
vector smoothing model. Much more realistic.
-Inland waters are moved to lakes and that allows radically faster water/ocean
polygons creation by remaining land polygons inversion.
-The land polygons data contain large number of small polygons of land-on-land
type.
-There are still several replicated consecutive nodes on land polygons.
-The global ocean (the large water) polygons still contain anomalies along the
World frame (inversion problems).
-Simplified water polygons are created by simplifying and inverting land
polygons. This is never the same as simplifying water polygons.
-The split polygon versions contain large overlaps and these for GIS and vector
map-makers present more trouble than good.
Finally I would strongly underline the following note. Using generalized
version of water polygons without synchronization with other object classes
(lakes, rivers, forests...) causes serious logical and aesthetic cartographic
problems. For instance, large objects in one class disappear while small
objects in other classes still are present (collapse synchronization), objects
with radically different details are connected or slightly overlap and so on.
An example of simplified water polygon and not simplified lake connection can
be seen here
https://osm.org/go/Z1a9HCF6g-?layers=TD&way=100084105 . This link also
illustrates the mentioned erroneous small polygons in the coastline land
polygons that are missing islands in lakes or rivers.
Sandor.
Sent from Mail for Windows 10
From: Joseph Eisenberg
Sent: 26 February 2019 04:10
To: talk@openstreetmap.org
Subject: [OSM-talk] Openstreetmap-carto switching to ocean polygons
There is a new PR on the Openstreetmap-carto Github page which will switch this
“standard” style (used on the main OSM page) to water polygons instead of land
polygons.
However, some users reported problems with the simplified water polygon
shapefiles when this change was attempted in 2016. We believe the problem is no
longer present, because the German map style is using these shapefiles without
problems, but it needs testing. If you were one of the affected users, please
try out the change on your server.
The branch is available at:
https://github.com/jeisenbe/openstreetmap-carto/tree/ocean-polygons
New PR:
https://github.com/gravitystorm/openstreetmap-carto/pull/3694
Old issue:
https://github.com/gravitystorm/openstreetmap-carto/issues/2101
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