Fungimap: mapping and grid references

Grr Grr--What do I do about grid references?

One of the main aims of a mapping scheme is to produce maps. Computer programs are now available that allow plotting of distributions at various scales, and with overlays such as rainfall or soil types. The mapping programs used by Fungimap work from latitude and longitude. Records can be submitted with various types of grid references, but all records will eventually need to have a latitude and longitude. Fortunately, other grid systems can be readily converted to latitude and longitude.
The level of precision used by Fungimap is to about the nearest 1 kilometre. So, latitude/longitude needs only to be given to the nearest minute (as for example 37deg.46'S, 145deg.09'E).

The Australian Mapping Grid (AMG)

For grid references from topographic maps (Natmap or other series), the best scale is 1:100,000, or a larger scale such as 1:50,000 or 1:25,000. Latitude/longitude can be worked out from these maps, but the values are usually only given along the edge of the map in intervals of 10 minutes (for 1:100,000 maps). The grids that are printed on these maps are the Australian Mapping Grid (AMG).

To give an AMG reference find the vertical grid line to the left of your locality (read off the number from the top or bottom of the map); if the locality is on a grid line place a zero at the end of this number, otherwise if the point is not on a grid line, estimate how far it lies between the grid lines on either side (a number between 1 and 9, with 5 being half way between two grid lines), and place this number after the first number. This gives a three digit number like 010 or 978. Repeat this process for the horizontal grids to give another three digit number. You then need to specify the map, which has a name and a number (ignore the letters identifying the 100,000 m square). Putting all that together gives something like 8022-Healesville- 742.280 (which is the water tower at Badger Creek).

There is a computer program which converts Australian Map Grid references to latitude and longitude, and for this the full grid references are required. For the example above, the full grid reference will be in the form 3742.57280 . Note that there is a prefix '3' for the vertical grid, and a prefix '57' for the horizontal grid. These prefixes are the small numbers in front of the normal grid numbers, and are given at the south west corner of the map, and usually every 10 grid lines. The prefixes change at 100, so be careful that the prefix applicable at one corner of the map is the same as that in other parts of the map. Some topographic maps I have seen have the prefix printed before every grid number, which is less confusing (if that is possible!).

When giving Australian Map Grid references, the complete form is, for example, 3742.57280 (for this you don't need the map name and number). If you want to give the reference in the basic form, write it as follows: 8022-Healesville-742.280 (the map number and map name, followed by a dash,with the vertical and horizontal coordinates separated by a full stop).

Alternatives

For metropolitan areas, street directories are also a good way of giving a grid reference. For the Melway, for example, just give the map page and the letter and number of the square. Where I am sitting at the moment in the National Herbarium of Victoria is Melway-2G-A12. Even better, the Melway has Australian Map Grid lines on each map; they are the very fine red dotted lines. The only tricky part can be when your location is at the edge of a map, and you can't see where the next AMG grid line is, but you can work out what the distance between grid lines is from the centre of the map. The grid numbers are given in the complete form (ie. with the prefixes). For the Herbarium the complete AMG reference is 3219.58108.

The Vicroads Country Directory also gives complete AMG grids (the fine blue dotted lines), and latitude and longitude (the red grid lines - but difficult to use because there are eight divisions within each 30' section and you need to interpolate to get the precise minutes).

A useful series of maps for Victoria are the ESMAPs. These are books which are produced for the use of emergency services such as the CFA and contain maps at a scale of 1:50,000 with the complete AMG grids marked. There are ESMAPs for various parts of the state, enquiries about availability can be directed to VICMAP marketing, (03) 9651 1814.

For out of the way places (which we hope that you will all be visiting and recording fungi at) the Readers Digest Atlas of Australia could be used. It is at a scale of 1:1,000,000, with a grid for latitude and longitude.

So, give a grid reference where you can, and remember that you only need to give just one sort of grid reference for each record!

Global Positioning Sysytem (GPS)

For those who have one, a GPS can tell you exactly where you are, saving you the bother of consulting a map. However, it is still important to record the location information carefully. A GPS can be set to display the location in either degrees, minutes and seconds (eg. 38deg10'30") or with the seconds as a decimal (eg. 38deg10.5'). For Fungimap purposes, the first method is preferable, however either system is acceptable as long as you clearly indicate on the record sheet which system you are using.

When all else fails...

If you are still saying grr to grids, and it all seems too complicated (and you don't feel like getting a degree in mapology), don't worry, in the absence of a grid reference, a reasonably specific descriptive locality is still useful - something like 50km north of Coober Pedy on the Stuart Hwy is fine. A photocopy of a map with an X marking the spot will also do (but only do this if you can't give a grid reference).

Last modified on 7 August 2003