Maps are often marked with a grid to aid the description of the location of specific features on the map. In the UK the commonly used Ordnance Survey maps with scales of 1:25000 and 1:50000 are printed with a grid of squares that represent an area 1 kilometre by 1 kilometre. On the map the squares have side lengths of 40mm or 20mm depending upon the scale. As a kilometre is a long distance it is usual to estimate the position of features to a tenth of this distance, 100 metres. With practice this can be done by eye but it is easier to do if a scale is available to measure to a tenth of a grid square. The usual device for this is called a romer, it takes various forms and it can be made quite easily.

Transparent Romer Card Romer

The romers shown have scales for both 1:25000 and 1:50000 scale maps. Romers can be printed on transparent acetate or white card, the card ones have to be trimmed so that the markings are along the edge of the card. If you want to make one right click on the romer PDF link at the bottom of this paragraph and select 'save target' to download the file, romer.pdf. This is a drawing for 15 romers on an A4 sheet. If you save this PDF file you can test print on ordinary paper using the Adobe Acrobat reader program. This allows you to check the dimensions are correct when you use your printer. Ten units on the 1:25000 scale should measure 40mm and ten units on the 1:50000 scale should measure 20mm. This test will avoid wasting the more expensive clear acetate sheet if there is a problem. This file can then be printed on card or clear acetate. Photo copying the romers is not usually a good idea because copiers often distort the dimensions slightly.

Romer PDF file link.

If you haven't got the Adobe Acrobat reader program it is available as a free download at

Once the printing is complete carefully cut out the romers. It is a good idea to cover the printed side of the romer with clear self-adhesive plastic sheet. This makes it more durable. To finish punch a small hole in it and attach a length of coloured wool. This is useful for attaching the romer to you or your map case so that you do not lose it.

If you are not familiar with the method of using grid references it is explained in the key panel on UK Ordance Survey maps.