Purpose of triangulation networks in national surveys: Triangulation surveys are primarily carried out to provide which type(s) of control for mapping and engineering?

Introduction / Context:
Before detailed mapping, a framework of control points is needed so that all subsequent measurements fit together. Triangulation (and today, GNSS) provides a precise network to which all detail can be referenced.

Given Data / Assumptions:

• An extensive survey area (regional or national).
• Classical triangulation using angles/sides, supplemented by trigonometric leveling for elevations.
• Control points will support detailed plane-table, total station, or photogrammetric work.

Concept / Approach:
Triangulation fixes positions (coordinates) of control points over large areas—this is planimetric control. The same network, combined with measured vertical angles or spirit-level connections, provides height control (trigonometric leveling). Hence, triangulation underpins both horizontal and vertical control, even if precise leveling later refines heights in critical projects.

Step-by-Step Solution:
Establish first/second-order triangles for robust planimetric framework.Measure vertical angles/baselines to compute elevations (heights) where required.Therefore, triangulation contributes to both planimetric and height control.

Verification / Alternative check:
Specifications often distinguish “horizontal control” (triangulation/GNSS) and “vertical control” (leveling), but trigonometric elevations from the same stations are standard, confirming dual utility.

Why Other Options Are Wrong:
Planimetric only / Height only: incomplete view of triangulation’s role.None/Magnetic control: not the purpose of triangulation networks.

Common Pitfalls:
Assuming height can be ignored—without vertical control, contours, drainage, and design elevations cannot be tied effectively.

Final Answer:
Both planimetric and height control.