Map Data Pre-process(4)

Enter the following URL
http://mt1.google.com/mt?n=404&v=w2.52&x=841&y=608&zoom=7

Google maps show the Perth city. We know that the latitude and longitude is near -31.9 , 115.9
And we know for zoom level=7 ,the whole map is divided into 1024X1024 tiles
So x (longitude) , y (latitude)
Let’s do some calculation
X=841
841/1024*360-180=115.6 (approximately 115.9) (the degree of whole circle is 360)
Y=608
608/1024*180-90 =16.875 (much smaller than 31.9) (the degree of half circle is 180)
So this is not a simple or linear relation between x,y and longitude and latitude. Google maps uses some kind map projection algorithm.
Search for the most popular map projection algorithm. And understand the fact that meridians and parallels are equidistance, straight lines. Google map uses Simple Cylindrical projection. This projection is also known as Lat/Lon WGS84.

With the WGS84 map projection algorithm, we know each tile’s longitude and latitude, so can covert to method 2’s format.