How to Date Ordnance Survey Maps

Do you have OS maps you are struggling to date accurately?

Although almost all OS maps have a date printed somewhere in the margins it is often not immediately obvious up to what year they are accurate.

This can be crucial if you are trying to make sense of a map in the context of family history, a structure you are trying to determine the date of or want to see when a feature such a railway disappeared.

Where is the date on an OS map?

location of date on an OS map
Location of Dates on a Popular Edition OS Map

Most OS maps published before about 1992 have the publication details printed either in the bottom right or bottom left. But that’s not the whole story.

Many OS maps have a date described as the date of publication and/or printing but also have compilation and/or revision dates as well as quantities printed at certain dates. 

It’s not always that simple, though. Quite often, on older OS maps especially, there are codes at the bottom left corner which indicate print/revision¬† dates.

Revision Dates

On many OS maps revision dates are, apparently, clearly stated. However, there is no consistency to how these revisions are expressed, even with the same series and even amongst maps of similar age.

1:25 000 Second Series, later the Pathfinder, map was produced in various styles of “cover” between 1965 and 1996. Although there were minor changes in representations on these maps they remained essentially the same throughout their life. But the revisions were expressed quite differently from one sheet/revision to another.

Compilation notes would usually include dates from which the map has been compiled from six-inch sheets or from 1:10 000 or 1:10 560 maps. This gives you a base revision date. Beyond that you might see “partially revised”, “revised for significant change(s)”, “selected revision”, “major roads revised”, “minor changes”. These can pose more questions than the information they provide. What, for example, constitutes “significant change”?

As a guide, major roads would be Motorways or A roads and minor revisions, or corrections would usually be where there are new buildings or minor boundary changes and the like.

On later Popular Edition maps a dating format was adopted which simply said, for example: “Published and printed 1923 with periodical corrected reprints”. Sometimes that’s all you will see whilst at other times you there will be a code in the left corner which might read something like “3036 M.36. R.33.”. This would mean that 3000 copies were printed in 1936 with Minor Corrections to 1936 and Roads Revised to 1933.

Magnetic Variation

On most OS maps the annual variation of magnetic north is described either with an illustration, as per this Popular Edition map, or simply in text at the bottom or side margin.

The date stated for the calculation of the magnetic variation can also give you a guide to the last revision of the map you are looking at in the absence of any further evidence.

This can be especially useful on maps such as the New Popular Edition which do not include specific revision dates in the margins.

However, you have to check all the other references on the map before you can confidently infer that the Magnetic Variation date is the last date of revision. I have plenty of maps on which the Magnetic Variation date is earlier than the latest stated revision date.

Unfortunately, in this respect, as in many others with Ordnance Survey maps, there is no consistency.

Mixed Signals

I am using Popular Edition maps quite a lot as examples because they display quite a good number of the inconsistencies and variations of revision references.

A Popular Edition Sheet 143 Truro & St Austell map that I have includes, at the bottom right corner:

“Engraved at the ORDNANCE SURVEY OFFICE Southampton,
Surveyed in 1866-81 and Published in 1877-90.
Revised in 1894 and in 1905-6
Revision (3rd Revision) 1913
Printed at the Ordnance Survey Office, Southampton 1918
Minor corrections 1930
3500/19. 1000/24. 3500/27. 4000/29. 5500/31.”

And towards the middle of the bottom margin:

“Roads revised to 9/24”, crossed through and, in red, “10/26”.

in the sea in the North West of the map the magnetic variation is stated to “Jan. 1927”.

The numbers “3500/19” and so on, are the quanties printed in that year.

So this information gathered together gives you an excellent picture of the revision history of the map.

Beware, though, as you can not be sure what was revised in each printing year. You might be forgiven for assuming that the last date that roads were revised was October 1926. However, it is entirely possible that (very) minor revisions to roads and other features were made before the last printing date stated, in this case 1931.

On the other hand you can not assume that any revisions were made after the date actually stated. Thus, when I advertise a map for sale I now state the date as the last date I can be certain of.

Map Covers

Map covers are reliable for dating maps only up to a point.

Within any one series (or edition) of OS maps a number of different covers were used – published at different dates.

John Paddy Browne’s excellent book “Map Cover Art”, published by the Charles Close Society, provides an illustrated list of OS map covers, the dates they were issued and on which maps. A more complete catalogue of OS maps covers, including dates and editions, can be found on the Charles Close Society website. However, the Ordnance Survey seemed to hate waste and very often they used new covers on older maps – an sometimes vice-versa.

In other cases, such as the 1:25 000 First Series maps, numerous sheets were not revised for many years. These were issued in a number of different covers (see “Guide to OS Maps“) but you can frequently find a map dated in, say, 954 in an integral “cover” which has clearly been printed much later.

I was once accused of selling facsimile maps because I was adverting a 1:25 000 First Series as a 1954 revision in a cover with a decimal currency price. But the map in question had been issued in four or five different covers over the years simple because it had not been revised.

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