Talk:Great Lakes

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Great Lakes disappear at lowzooms

At zooms <=5 the Great Lakes disappear with Standard/mapnik. OSM seems to draw the Black and Caspian Seas ("landlocked" large inland bodies of water, variously called Lake or Sea) properly at lowzooms. Can this be fixed? I know these are highly complex structures in super-relations (and I understand those well) and that part of certain coastline was changed. Is there a "bug report" place in OSM where it's better to discuss this? Apologies in advance if this got discussed somewhere else and I missed it, if so please point me there. Stevea (talk) 02:55, 17 October 2016 (UTC)

Great Lakes are not seas (like the Black and Caspian Seas that are delimtied by coastlines). They are lakes, and lakes in land are not rendered, independantly of their size. This is the same case with the Baikal Lake in Russia (between regions RU-IRK and RU-BU), or large lakes in Africa (notably those around Tanzania and Uganda), or Geneva Lake/Lac Léman between France and Switzerland). The Back sea is not completely landlocked,, it communicates with the Mediterranean Sea and thhe Atlantic Ocean. The Caspian Sea is full landlocked but is tagged using coastlines (with natural=coastline), the lakes are tagged as polygonal water surfaces connected to other water surfaces of their rivers crossing them and flowing down to the sea through the land.
The good question is then: should those very large lakes be tagges like seas with coastlines ? I think not because they are not salted (their water is renewed), however Lake Baikal in Russia should be considered as a sea (water does not exit it, and it has a high concentration of salt in its very deep waters). Great Lakes in North America, Lake Victoria in Africa and Lake Baikal in Russia however could be marked using coastlines given their huge size and the complexity of their very long borders, and hte fact that they create sea-like meteorological conditions, just like the Caspian Sea, even if they are not reached by large oceanic streams caused by Earth rotation, they are still slighly affected by circular streams created internally by Earth rotation (but more importantly by temperature differences between the warmer surface and cold deep waters in their center and variations across seasons, the effect being more visiblle in the Tropical area where the Caspian Sea is located, but much not noticeable in Great Lakes and Lake Baikal). — Verdy_p (talk) 04:24, 18 October 2016 (UTC)
Okay- the lakes aren't salty, so they aren't seas. What they ARE are giant bodies of water that should show up at all levels of zoom. The sodium content of a body of water shouldn't matter when you're talking maps, the size should. Almost every outline of the United States includes the great lakes - they are a part of the shape of the country and should be represented. Y'all are smart people, every other mapping solution has figured it out, I'm sure you guys can too. Right now, I have major highways- tiny strips of asphalt showing up before massive bodies of water that are larger than several states. That's wrong. — --Amoliski (talk) 17:19, 11 October 2017 (UTC)
You're spekaing here about rendering, this is a rendering issue (e.g. roads over large lakes on bridges, shown before these lakes: this is a rendering issue, and up to renderers to adapt what they will show to the actual size of features, and not just to how they are tagged.
May be we could have a more specific tag for large lakes (like the 3 Great lakes in USA/Canada, Lake Chad, Lake Victoria, Lake Baikal, Lake Leman, and even Tiberiad Lake on the Jourdain River, the Dead Sea, and the smaller lakes that have replaced the Aral Sea previously connected to the Black Sea, and that are crossed by an international border) to ease their rendering in priority to roads and international borders, and to be drawn just after drawing seas. Still these lakes are not bordered by "coastal lines".
The same question remains for large glaciers and iceshelves, including on the Antarctic or Greenland, or in large mountain chains (e.g. in South America), where computing their actual area is very coastly when they span an area much larger than a single "metatile" in Mapnik.
But renderers are not working directly on OSM data, they extract features in a GIS database (computing geometries like [Multi]Polygon in GeoJSON) and precompute at least their bounding box; if the bounding box is large enough, the actual area may be computed and stored, to allow their renderers to render them at lower zoom levels: this should not require any specific tagging, it will be automatic.
This should also apply to linear features ([Multi]MultiLineSting in GeoJSON), but we use some selecitve tags: admin boundaries are shown accordint to their admin_level, roads according to their classification (motorway|_link], trunk[_link], primary[_link], secondary[_link], tertiary[_link], residential and unclassified, then cycleways, and finally paths and footways, rather than just their measured length. This also applies to rivers, canals and then streams and ditches.
For node only features (such as admin centers they will be shown according to other specific tags, such as their "admin_centre" role in boundary relation, the admin_level, or the population tagged in that boundary. — Verdy_p (talk) 19:39, 12 October 2017 (UTC)