Each nation decided its own reference system long ago, before nuclear ICBMs made global positioning necessary. Any reference to coordinates is within a system, so you need to know what reference is used, then convert to one system. WGS84 is the current global system employed by GPS. There are converter utilities online.

Google Earth (GE) is accurate to within 30 miles in Greenland, but noone is paying much attention to that icy world.

High resolution image areas are typically very accurate. You can compare my GPS readings at Cahokia and Ohio mounds:

[jqjacobs.net]

GE coordinates are certainly useful and better than no coordinates. However, GE is developing, so I recommended referencing them by date. I use the convention "GE 2006-11-15" for today. This is an equivalent to "date accessed" in referencing websites.

So, what portion of our 360 degree world is presented by the Khufu to Snefru arc? The same amount, no matter the reference system!