I'll gladly be in the minority. The fact that it literally has the same moon as ours, same sun, and same planetary system as ours makes me believe it's our earth

Bottom Right Panel
River = 3 pixels
Alabasta = 208 pixels
Alabasta/River = 69.333
River = 50,000 meters (its from here)
Alabasta = 3,466,650 meters
Top Left Panel
Alabasta = 23 pixels
Distance Between Islands = 182 pixels
Distance Between Islands/Alabasta = 7.913
Distance Between Islands = 27,431,601.45 meters

Why not just scale directly from Alabasta? If you noticed above? There are no islands large enough near Alabasta to be visible from our bird's eye view. To account for this, we need to scale from the distance between islands on the Grand Line as shown on the globe. Where I scaled is likely not even Alabasta, but the odds are pretty good that Alabasta's not even an island large enough to be seen on the scale of the globe anyway.
Distance Between Islands = 6 pixels
Planet Diameter = 99 pixels
Planet Diameter/Distance Between Islands = 16.5
Planet Diameter = 452,621,423.925 meters

Upper Yard = 355 pixels
Jaya = 262 pixels
Jaya/Upper Yard = 0.738
Upper Yard = 10,476.48 meters (found above)
Jaya = 7,731.642 meters

Jaya = 398 pixels
Jaya Height = 36 pixels
Jaya Height/Jaya = 0.09
Jaya Height = 695.848 meters
None of this height peaks over the horizon for Ussop to observe.
Planet Diameter = 452,621.424 kilometers