A six-figure grid reference pins a point within a grid square. Start with the two grid lines that bound the square, then add a tenth for each direction.
This lesson opens topographic direction and position and uses the eastings before northings rule from scale, direction and grid references.
How do I build a six-figure reference?
Follow four steps.
- Read the easting line to the left of the feature, such as 42.
- Estimate how many tenths across to the feature, such as 3. Write 423.
- Read the northing line below the feature, such as 57.
- Estimate the tenths up, such as 8. Write 578, then join: 423578.
The tenths are fractions of the square width. A feature in the middle is 5.
Worked example: an original water tower
An original map has a water tower inside the square bounded by easting 42 and 43, and northing 57 and 58. The tower lies about three-tenths across from the left line and eight-tenths up from the bottom line.
Four-figure reference: 4257. This names the whole square, where the lower left corner is at 42 and 57.
Six-figure reference: easting 42 plus three-tenths gives 423. Northing 57 plus eight-tenths gives 578. The reference is 423578.
The four-figure reference fits many points in the square. The six-figure one identifies the tower.
The mistake: adding tenths to the wrong line
A typical error is measuring the tenths from the right-hand line instead of the left. A tower that is three-tenths from the left line is seven-tenths from the right line, giving 427, which is a different point.
Always measure from the left line for eastings and the bottom line for northings. A ruler marked in tenths of the grid width makes this reliable.
| Step | Wrong | Right |
|---|---|---|
| Easting tenth | Measured from right line: 7 | Measured from left line: 3 |
| Northing tenth | Measured from top line: 2 | Measured from bottom line: 8 |
| Reference | 427572 | 423578 |
Check yourself
A bridge lies in the square between easting 38 and 39 and northing 61 and 62. It is half-way across and two-tenths up. Give the four-figure and six-figure references.
Answer
Four-figure: 3861.
Six-figure: easting 38 and half (5) gives 385. Northing 61 and two-tenths gives 612. The reference is 385612.
What to study next
Continue with measuring a bearing from a stated north line, which uses the same grid lines.
For a teacher to check your measuring, see online one-to-one Geography tuition.