What direction is determined from the mathematical approximation of the Earth's shape?

Geodetic North refers to the direction aligned with the Earth's mathematical model, which is based on a geoid or an ellipsoidal shape that represents mean sea level across the globe. This concept of Geodetic North is crucial in surveying and mapping as it provides a consistent reference point for accurately determining positions on the Earth's surface.

Unlike True North, which is based on the Earth's rotational axis and can vary slightly due to tectonic shifts, Geodetic North uses a standard model of the Earth’s surface, ensuring uniformity in navigation and data collection.

Magnetic North varies due to the Earth's magnetic field and can change over time based on magnetic fluctuations, while Grid North relates specifically to how maps are oriented to a grid system and can differ from the other north references depending on the scale and projection used. Thus, understanding Geodetic North is foundational for surveyors, as it allows for precise calculations, alignments, and comparisons across various geographic locations.