Grid Reference

Grid References

Grid references define locations in maps using Cartesian coordinates. Grid lines on maps define the coordinate system, and are numbered to provide a unique reference to each location on the map. This reference is normally based on projected eastings and northings. 

A grid reference system is a simplified grid used for a map area to make reporting and looking up coordinates easier.
In a grid reference system each grid line on the x axis and y axis is labelled sequentially with a two-digit number(much like a graph). Gridlines may be 10,000, 1000, 100m apart. We estimate or measure the position of the points between two grid lines. As with most coordinate systems we report Easting followed by Northing.

In the example below the “T” is at 042 066

In a grid reference system the number of significant figures indicates the precision of positions. So we could also report “T” as 0424 0662 if we measured it more precisely.

Grid reference systems are good for:

1. reducing the number of digits needed to identify a position on a map
2. representing the precision of a measurement
3. making it easier to look up and report positions

They are bad because they:

1. obfuscate the underlying coordinate system
2. need to be converted to full grid reference coordinates to use in GIS

Quick Recap on Grid Reference