National control networks and accurate mapping: surveys conducted to provide a national grid of control for accurate mapping of large areas are known as:

Introduction / Context:
Large-scale mapping over countries requires a high-precision framework to which all detailed surveys can be referenced. This framework accounts for the Earth’s curvature and uses rigorous adjustment of long baselines and angles.

Given Data / Assumptions:

• Objective is to establish control across large regions or an entire nation.
• Accuracy requirements extend beyond plane approximations.
• Results serve as the basis for topographic mapping and engineering projects.

Concept / Approach:

Geodetic surveys create high-order control networks using triangulation, trilateration, GNSS, and precise leveling, all adjusted on a reference ellipsoid/terrestrial reference frame. Plane surveys assume a flat Earth over small areas and are unsuitable for national grids.

Step-by-Step Solution:

Verification / Alternative check:

National mapping agencies explicitly refer to geodetic control networks or geodetic reference frameworks as the basis for their grids.

Why Other Options Are Wrong:

Plane surveys neglect curvature; geographical is not a standard survey class; topographical describes map content, not the control framework; cadastral focuses on property limits.

Common Pitfalls:

Confusing geodetic control (framework) with topographic mapping (content); assuming plane methods scale to national extents.

Final Answer:

Geodetic surveys