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 metres (six-figure references) or even 10 metres (ten figures). 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 online method 1, works fairly well on tablets and smartphones

Step 1
Go to

Step 2
Put in either your postcode (if it's your house) or a place name into the appropriate box. Then you can move the map and zoom in on the aerial view to pinpoint the spot.

Step 3
Right-click (on a computer) or hold your finger (tablet/phone) on the exact point to put a pin in the map. If you get it wrong delete it from the list below the map (cross at the end of the line) and do it again.

Step 4
The full 10-figure grid reference appears (shown in orange). You can copy and paste this from a computer, but on a tablet/phone it's easier to copy the 'Link to all points' at the bottom by holding your finger on it, Paste into my box again by holding your finger on it.

Online method 2

Step 1
Go to using this link

Step 2
Type in the name of the place, road, postcode, or even geographical feature like a wood, 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.)

Step 3
Move the arrow at the centre of the map to the exact spot by clicking on 'Move Arrow' and then on the correct spot, then copy all the figures in the search box at lower left of the map and paste them into the survey form. If this doesn't work (maybe if you are using a Mac) then just copy and paste the location of the map (the http address in the location bar, not the whole page). Tablet and iPad users, press your finger over the thing you want to copy and it should be highlighted, or there will be movable markers to allow you to highlight more or less. A dialog should appear at the top of the page which allows you to copy or paste.

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 SU513827 (Blewbury Down in Oxfordshire – I chose the numbers completely at random, and I have had no reports from the exact spot, but it would be a very good site to investigate anyway!).

Alternatively, you can go to the Ordnance Survey website, 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, as is a Google Earth placemark or a postcode, though not as convenient as a grid reference.