Formula and method
Euclidean distance is √[(x₂ − x₁)² + (y₂ − y₁)²], adding (z₂ − z₁)² in 3D. Geographic mode uses the haversine formula on a sphere of radius 6,371.0088 km.
Worked example
Points (0, 0) and (3, 4) are √(9 + 16) = 5 coordinate units apart.