It describes the intersection of two lines. Ignoring the small numbers either side of the black numbers (explained later), notice that the lines increase by one unit along the bottom (68, 69, 70, 71…) and up the left-hand side of the map (05, 06, 07, 08…).Ī four digit grid reference (2 digits for the Easting, and 2 for the Northing) is a crude measure of the location with an accuracy of one square kilometre. The Northing and Easting lines are all numbered. On the 1:25,000 map above, each square is 1km wide and high. In this example, since the hill has no name it can be called Hill 619. Often, bushwalkers describe a hill by its height, unless another name is written on the map (typical for popular and distinctive hills). The 619 refers to the height of the hill in metres. A simple way to remember this is the saying ‘ cross the creek before going up the tree’, that is, go horizontal first, then vertical.Įxample 1: Describing the location of the hill labelled 619. When reading a grid reference, Eastings always come first, followed by the Northings. The more digits, the more accurate the grid reference. Determine the number of Eastings and Northings digits by dividing the whole grid coordinate by 2. It consists of two parts – the Easting digits, and the Northing digits – and always has an even number of digits. a reading in degrees, minutes and seconds).Ī UTM grid reference tells the reader how East and how far North to go on the map. Most maps also include the Longitude and Latitude of the map at the corners (i.e. they establish how far north the point is). ![]() they help locate how far east the point is), and the horizontal lines are called Northings (i.e. ![]() ![]() In the UTM system, the vertical lines are called Eastings (i.e. The Universal Transverse Mercator (UTM) system, which describes a point in terms of metres, is most commonly used by modern topographic maps. The vertical lines are aligned with grid north, and the horizontal ones are exactly perpendicular to the vertical lines. Maps have numbered vertical and horizontal grid lines that enable the reader to identify and communicate a particular location on the map. In an emergency, it may be possible to get enough mobile phone coverage to contact the emergency services and communicate the location of rescue. That’s why it’s important to communicate which reference system is being used and to know how to convert between them. While being off by 200 metres doesn’t sound like much, in the bush this can be disastrous for an emergency operation, or cost a bushwalking party serious time delay. The result of the change from the AMG system to the MGA system is a shift of approximately 200 metres in a northeasterly direction. The AMG system was used until roughly the mid-90s when it was replaced with the MGA system, which is more compatible worldwide as the GDA 94 datum is almost identical to the WGS84 datum used in GPS (Global Positioning Systems). The MGA reference system uses the Universal Transverse Mercator projection of the Geocentric Datum of Australia 1994 (GDA94). As a general rule, all the new series maps have an aerial photo image on the reverse. MGA: The MGA is the Map Grid of Australia 1994, and is used in all the new series maps.The AMG reference system uses the Universal Transverse Mercator projection of the Australian Geodetic Datum 1966. AMG: The AMG is the Australian Map Grid 1966/1984 system and was used on the old series maps, mostly distributed circa the 1980s.In NSW, the 1:25000 topographic maps use either the AMG or the MGA coordinate systems. When communicating a grid coordinate, state the coordinate system first, then the grid coordinates. ![]() Maps usually have an information section that identifies the map datum and projection, along with the publisher and copyright information. Two points can be out by as little as a few hundred metres, or as much as several kilometres if there is confusion over the reference system in use. Any given reference system is based on a datum, a 3D representation of the earth, and datums differ in how they represent land and where the location of the central frame is.
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