How to work out a Grid Reference
|The National Grid system works on a
system of squares of differing sizes.
First, the whole country is split into squares of 100km by 100km. Worcestershire falls into two of these: SP and SO. The red dot is in SP. Places to the right of the 00 line are in SO.
The black lines split the area into 10 km squares, and the red dot falls into 10 km square SP85 - the 8 is from the top or bottom edge of the map, and the 5 from either side.
The blue lines split the area into 1 km squares, and the red dot falls in square SP8254 - the 82 again from the bottom or top of the map, and the 54 from one or other side.
|If you give a grid reference for the 1km square where you found your specimen, this will be accurate enough for many records. All of the 1:50 000 Landranger maps and the 1:25 000 Explorer maps have 1 km squares drawn on them (in black, not blue like these), and the numbers for the squares along the top, bottom and sides, as well as somewhere in the middle to make life easier.|
|To remember which number to quote first, think that you have to go 'in through the door' , that is across the map, before you go 'up the stairs'.|
|If you need to give a more accurate grid reference for something rare, then you have to imagine that your 1 km square is divided yet again into 100 metre squares - 10 squares in each direction, as shown by the yellow lines, and then add an extra number in each direction. The red dot is now in SP 828 542. This is a six-figure grid reference.|
There is a device called a 'romer' with the numbers marked along two sides at right -angles which make this job easier. You can get a free one if you buy your maps at the Map Shop at Upton-on-Severn.