What was the basis for angles measured during the Mexican Period?

The correct basis for angles measured during the Mexican Period was True North. During this period, surveyors relied on True North as a reference point for their measurements. True North is defined as the direction along the Earth's surface towards the geographic North Pole, which is a consistent reference for establishing bearings and orienting maps accurately regardless of local magnetic declination.

Measurements based on True North allow for precise mapping and reduce discrepancies that could arise in surveying due to variations in magnetic fields, which can cause error when using Magnetic North. This is particularly important for land surveying, where accurate boundaries and descriptions are crucial for legal and property rights. The use of True North provides a standardized method that remains constant over time, unlike Magnetic North, which shifts due to changes in the Earth's magnetic field.

Understanding this context helps in grasping why True North was favored during the Mexican Period for land surveying, as the outcomes of these measurements were pivotal in the context of land grants, property claims, and the establishment of boundaries during that era.