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### 1. Defining a Grid Coordinate System

A grid coordinate system must be carefully designed to ensure that:

- grid and horizontal ground distances match
- grid and horizontal ground angles match.

These, in turn, preserve shape and area of measured quantities.

An "ideal" grid coordinate system should have these three characteristics:

#### a. Orthogonal

The system consists of two reference axes are right angles to each other, Figure C-1

Figure C-1 Reference Axes |

These define Grid North and Grid East for the system.

#### b. Parallel meridians

All meridians are parallel with the North reference axis, Figure C-2, with no convergence.

Figure C-2 Parallel Meridians |

Forward and back grid directions always differ by exactly 180°.

#### c. Uniform scale

A linear unit is the same physical length regardless its orientation, Figure C-3.

Figure C-3 Uniform Scale |