[talk-au] Zoom levels

[John Smith]

I finally figured out what the zoom levels equate to in metres per pixel, although it's probably 100ths or 1000ths of metres per pixel judging by z18.

z0 => 313774583-627549167
z1 => 156887291-313774583
z2 => 78443645-156887291
z3 => 39221822-78443645
z4 => 19610911-39221822
z5 => 9805455-19610911
z6 => 4902727-9805455
z7 => 2451363-4902727
z8 => 1225681-2451363
z9 => 612840-1225681
z10 => 306420-612840
z11 => 153210-306420
z12 => 76605-153210
z13 => 38302-76605
z14 => 19151-38302
z15 => 9575-19151
z16 => 4787-9575
z17 => 2393-4787
z18 => 1196-2393