One of the most intriguing Ordnance Survey map series in the National Library of Scotland’s collection is the 1:500 Town Plans (as well as some at a scale of 1:528). These were produced in the latter half of the 19th century and very early 20th century, and cover most towns with a population over around 4,000 at the time of the survey.
The detail is astonishing, allowing for the inclusion of miniscule information that was not published elsewhere, such as lamp posts (LP) and man holes (WP). The Dundee town plan (below) contains this level of detail. One must be aware, however, that information can vary from town to town: in one town, railways may be shown in detail, whereas on another such fine detail may be omitted. Indeed, even banks and newspaper offices may not be shown.
Some of the more sensitive detail appears to have been omitted for reasons of security, most notably related to prisons and barracks. This is highlighted by comparing and contrasting two maps of Perth covering the same geographic area, and both dated 30th September 1863 (see the note below regarding the survey date). The upper image shows the prison in great detail, with the structure depicted and the rooms within that structure denoted. The image below it omits this information, showing only a blank area with text denoting the fact that a prison exists on the site.
But such omission of detail is not a 19th century anomaly. It occurs frequently on 20th century maps, especially in relation to sensitive military installations. It can even be seen in this aerial photograph of the area covering East Fortune Airfield. Taken in the period of time between the Second World War and the Cold War, the airfield has been completely eradicated.
One must also be wary of the survey dates. Whilst, on most surveys, these generally relate to the date of the actual survey, on the 1:500 town plans it can be the date the manuscript was certified for publication (with some investigations suggesting there could be two or three years between the actual survey and the survey date).
Staff at the National Library of Scotland have scanned all of the detailed 1:500 town plans for Scotland, and are in the process of scanning those for England and Wales.
For further information see:
Richard Oliver, Ordnance Survey Maps: A Concise Guide for Historians (2nd ed., revised and expanded), The Charles Close Society, London, 2005, pp30-32
John Moore, The Ordnance Survey 1:500 town plan of Glasgow: a study of large-scale mapping, departmental policy and local opinion, in The Cartographic Journal, 32, 1995, pp24-32