What is the Difference Between Grid North and True North?
🆚 Go to Comparative Table 🆚The difference between Grid North and True North is a result of the transformation from the Earth's spherical surface to a plane surface during map projection. There are three main types of north: True North, Grid North, and Magnetic North.
- True North (Geodetic North): This refers to the direction along the surface of the Earth that leads to the North Pole. It is the direction of a line of longitude, which converges at the North Pole.
- Grid North: This is the direction of a plane grid system, usually associated with the map projection. Grid North is aligned to grid lines and always points upwards on a map. The difference between Grid North and True North depends on the projection and the map's location relative to the projection origin.
- Magnetic North: This is the direction where the Earth's magnetic field points vertically downward. The location of Magnetic North changes with time and location on Earth's surface. The angle formed by the compass's deviation from True North is known as "declination".
For most navigation purposes, the difference between Grid North and True North can be ignored. However, depending on the map one is working with, understanding the differences between these types of north is essential for accurate interpretation and navigation.
Comparative Table: Grid North vs True North
The difference between Grid North and True North can be summarized in the following table:
| Aspect | Grid North | True North |
|---|---|---|
| Definition | Grid North refers to the direction northward along the grid lines of a map projection, such as the transverse Mercator projection. True North is the direction along the Earth's surface towards the north pole. | |
| Properties | - Grid North is constant and does not vary with location. - Grid North is always the same direction everywhere on every flat map. |
- True North varies with location on Earth. - Lines that run true north and south on Earth correspond to meridians and parallels, respectively. |
| Map Reading | - In small scale and medium scale maps, Grid North is considered. - Grid North can be adjusted to align with True North in some cases, but it is not always true north. |
- True North is the direction that corresponds to the Earth's north pole and is used for orientation purposes. - The angular difference between True North and Magnetic North is known as magnetic declination. |
In some cases, you may need to calculate the difference between Grid North and True North. This can be done using the magnetic declination, which is the angle on the horizontal plane between magnetic north and true north. The magnetic declination can be measured by instruments or obtained from models like The World Magnetic Model.
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