Geoid and Mean sea level differences[править]

The geoid is the shape that the surface of the oceans would take under the influence of Earth's gravity and rotation alone, in the absence of other influences such as winds and tides... the geoid's variation ranges from +85 m (Iceland) to −106 m (southern India), less than 200 m total compared to a perfect mathematical ellipsoid.

In aviation, the ellipsoid known as World Geodetic System 84 is increasingly used to define heights; however, differences up to 100 metres (328 feet) exist between this ellipsoid height and mean tidal height. The alternative is to use a geoid-based vertical datum such as NAVD88... The location-dependent, but persistent in time, separation between mean sea level and the geoid is referred to as (stationary) ocean surface topography. It varies globally in a range of ± 2 m.

Data[править]

free terrain data for anywhere in the world

aw:Aster instrument of the Terra satellite is also freely available for 99% of the globe, and represents elevation at 30 meter resolution... When land topography and bathymetry is combined, a truly Global Relief Model is obtained... ALOS provides since 2016 a global 1-arc second DSM free of charge... OpenTopography is a community access resource of high-resolution

http://www.opendem.info

aw:Category:Elevation api[править]

rivers[править]

реки в русской википедии имеют данные про водоток (исток, устье); расположение (притоки, населенные пункты)

• Wikidata has 'river mouth', 'river source' coordinates
• mw:Extension:Maps gives middle coordinates by geocoding
• World Rivers visualization on basis of aw:Natural Earth
  • lakes with rivers good
• Sources... Rivers : Demis
• we first download the simplified shapefile of rivers polygons from the OpenStreetMapData page - poor data but good idea