There have been some notable maps produced of the Wall, starting with Horsley, but arguably reaching a peak under the auspices of the Ordnance Survey, with their 2nd edition of the Hadrian’s Wall Two-Inch Map in 1972. This incorporated overlaid detail of the line of the curtain wall, ditch, Vallum, and military way, as well as the turrets, milecastles, and forts, distinguishing through colour both the visible (black) and the hidden (red) parts of the monument, as well as indicating where a degree of supposition was involved by means of broken lines. This has now been updated and, in part, replaced by the English Heritage Archaeological Map (see Bookshop).
The present atlas is being made available as a Google Earth KMZ file, embedded Google Maps, and Microsoft Bing Maps links. The three technologies differ considerably: whilst Google Earth holds the data as an XML file on your computer, Microsoft’s Bing Maps stores it on a remote server and, crucially, has a limit of 200 items in any one Collection, requiring several Collections to cover all the features of the Wall. Until this is remedied, this severely limits the usefulness of the Microsoft version for the purposes of comparing the various components of the Wall. Details of how to use these two systems are included below. Google Maps, meantime, looks up the KMZ file here on Per Lineam Valli and interprets it for you in two dimensions.