How to give a grid reference
The Ordnance Survey map references to glow worm sites are very important,
as they enable us to locate its position to within 100 yards. If we want
to check how numbers are varying in the future, this is essential – but
private sites will not be visited without permission and details are not made public!
Easy method
These days, online maps make finding a map references a doddle. My favourite is www.streetmap.co.uk.
You just type in the name of the place, road, postcode, or even geographical
feature, and the map appears after giving you a choice if necessary. (TIP: You may have to click on the – sign to get the Ordnance Survey map.) Click
on the exact spot, then read off either the figures in the box below,
or ideally click on the link at the bottom of the panel where it says
‘Click here to
convert/measure coordinates’ and give us the LR (Landranger)
coordinates, which are two letters and six figures.
The old method, using an OS map
If you have an OS map, instructions on giving map references are shown
in the margin. But basically, this is what you do. The map is divided into
1 km squares by grid lines numbered along the edges. You have to look along
the bottom or top edges first and find the number of the square, then estimate
the site’s exact position in tenths of a square. Then you do the same along
the left or right edges. The numbers are also printed every so often on
the map, which makes things easier:
The position shown has a six-figure reference of 513827. To complete the
reference, you need the two letters which are given in a key somewhere
at the bottom of the map, so the full reference might be ST513827 (Blewbury
Down in Oxfordshire – I chose the numbers completely at random, and I have
had no reports from there, but it would be a very good site to investigate
anyway!).
Alternatively, you can go to the Ordnance
Survey website, http://www.ordnancesurvey.co.uk/.
Go to ‘Get-a-Map’, where you will be able to fill in the place name or
postcode of the location and see a small-scale map of the area. Click on
the big + sign to the left and you will get a more detailed section of
the 1:50,000 map. You can also move around using the direction arrows to
the left. Below the map you will see the grid reference of the centre of
the map itself. Use the instructions above to work out the reference to
your site, bearing in mind that the figures increase from left to right
and from bottom to top.
Finally, latitude and longitude from GPS satnav units are OK, though not as convenient as a grid reference.
