To use the calculator, simply enter the latitudes and longitudes of the two points you wish to measure, and the calculator will provide you with the distances in both scenarios.
The Earth Distance Calculator uses the Haversine formula to calculate the distance between two points on the Earth's surface, taking into account the curvature of the Earth. This method provides accurate results for shorter distances, up to a few thousand kilometers. However, for longer distances, the curvature of the Earth becomes more significant, and the result will be less accurate.
For the distance through the Earth's core, the calculator assumes that the Earth is a perfect sphere, with a radius of approximately 6,371 kilometers. It calculates the distance between the two points as if they were connected by a straight tunnel passing through the Earth's core. While this is a theoretical distance that cannot be traveled by humans, it's an interesting way to visualize the distance between two points, for example, on opposite sides of the Earth. I used New York and San Francisco coordinates as default coordinates. Formulas used by the calculator are described here and here.
By the way, the longest distance you can travel on the Earth's surface without crossing water is a journey from Liberia in West Africa to China. This distance covers a total of 13,589 kilometers (8,439 miles), passing through 16 different countries.