Mercator Projection
zoom=17 -- 200x200
sides just reach each other (+-180 long)
middle is 0 degrees -- Greenwich Meridian
middle is equator
zooming in is 2x
The northwestern most tile is always 0,0 and x,y increase by one

* easy to convert x,y -> ttqs etc.

highest is 1 "mpp" MERCATOR.


therefore top must be 85.051128779806582259 = DEMARCLAT(180)