Clarify minimum area units

[pnorman]

boundary label minimum areas are given in km², but it's not clear if these are real kilometers, or mercator kilometers.

[pnorman]

It's also not clear if it's the area of the feature, or for disjoint multipolygons, the area of the particular area. I suspect the former

[pnorman]

#9 can be expanded to cover this
nevermind, parts of that have to wait for 2.0

[pnorman]

For the purposes of something to vote on, I propose converting all areas values in the spec to square meters, measured in web mercator. This would not change the way_area where it is in "ha", as that requires 2.0

[joto]

The area is mentioned in the spec for water_polygons and water_polygons_labels as way_area, area in square meter (Mercator Projection)" and for boundary_labels as "area in ha". But in the "Features" table the minimum area is given as "km²".

So we already have what @pnorman proposed for water polygons, nothing to change there.

For boundary labels we have to decide whether a change would be a clarification only or a real change. What did implementors implement here? ha or km²? osm2pgsql themeparks writes the area as "real" (spherical area) in m².