[OSM-talk] How much water on the planet?

[Frederik Ramm]

Hi,

    for various how-many-tiles-are-there calculations I used to compute 
the total number of tiles and then say "70% is water".

Just now I was curious to find out how much water there is in our 
spherical Mercator projection. Turns out that the "root tile" at z0 has...

    r     g     b   	 lum 	 count
  ----- ----- ----- 	-----	-------
    181   209   206	  200	  39482
    233   234   227	  233	  26054

... exactly 39482 / 65536 = 60% of water. But if I remove Antarctica 
(i.e. count it as water too) then the figure is almost 80%. So it is 
probably a realistic assumption that only 20% of Earth's surface have to 
be considered "interesting" for the purpose of creating surface tiles.

Bye
Frederik