Locating features on a map: area and grid references
It is an important skill to be able to locate places on a map. Many people use mapping skills in their daily lives. This chapter explains how to use area and grid references on topographic maps, as well as how to locate features on a street map.
Why use map references?
While the coordinate system of latitude and longitude is useful for officially and accurately locating places on small scale maps (show a larger area in less detail), it is not necessarily ideal for finding specific features on large scale maps (smaller area in more detail). It would be difficult, for example, to precisely explain the location of two separate features if they both had the same latitudinal and longitudinal coordinates. To enable people to better explain or define the location of features on large scale maps, area and grid references were devised.
What are area and grid references?
Topographic maps show the specific details of surface features in a relatively small area on the ground. Topographic maps often feature area and grid references, since it is an ideal way to systematically and accurately locate specific points.
Maps which use area and grid references feature a number of horizontal and vertical lines, which form grid squares. Each line is identified by a two-figure number, which appears in consecutive (following one another) and ascending (moving upward) order. The grid numbers on the east-west (horizontal) axis are called Eastings, and the grid numbers on the north-south (vertical) axis are called Northings. Eastings are always provided before Northings. In the following grid reference 6999, 69 is the Easting and 99 is the Northing.
When using eastings and northings, there are two important rules to follow. Firstly, always start from the bottom left hand corner of the grid squares. Secondly, the easting always comes before the northing when stating a location.
Finding an area reference
People sometimes need to find a general area, rather than a specific point on a map. An area reference allows people to find a general location in a grid square. Area references comprise four-figure numbers. The first two figures are always an easting and the second two figures are always a northing. To better clarify the type of reference it is, the letters 'AR' (area reference) are commonly placed in front of the four figures.
Using the topographic map below, the area reference of the red square would be AR0306. The first figure is 3, because the red square is located in the easting grid square of 03. The second figure is 06, since the red square is located in the northing grid square of 6.
See image 1
Finding a grid reference
Grid references are useful when trying to locate a specific point on a topographic map. Grid references comprise six-figure numbers. Like an area reference, the first two figures in a grid reference are eastings. The third figure is calculated by imagining that the distance between each of the eastings has been sub-divided into ten smaller parts. The figure is an estimation equivalent to how many tenths past that easting this point is. The fourth and fifth figures are northings and the sixth figure is an estimation of how many tenths past the northing that the point is located. For clarification purposes, the letters 'GR' (grid reference) are usually placed in front of the six figures.
Using the topographic map below, the grid reference of the red square would be GR038065. The first two figures are 0 and 3, because the red square is located in the easting grid square of 3. The third figure is 8, since the red square is approximately eight-tenths of the way past the easting of 3.
The fourth and fifth figures are 0 and 6, since the tree is located in the northing grid square of 6. The sixth figure is 5, because the red square is approximately half way past the northing of 6.
See image 2
The system of latitude and longitude is not ideal for street directories, since street maps (like topographic maps) tend to feature a relatively small ground area. Area and grid references used in topographic maps, however, are also not suitable for street directories. Topographic maps are usually used by people who have specialist skills to interpret maps, whereas street directories are used by many different people.
Some street directories use grid squares as a part of its reference system, while others require the reader to imagine where the horizontal and vertical lines extend to. All street directories feature numbers along the vertical axis. Unlike area and grid references on topographic maps, however, street directories also use letters to label grid lines along the horizontal axis. This way, coordinates cannot be easily confused.
To locate a place on a street map, references are written in the form of a letter followed by a number. On the street map below, the church corresponds with the horizontal axis point E and the vertical axis point 11. This means that the reference for the church is E11.
See image 3