These maps were compiled or collected by the Ordnance Office, the Ordnance Survey, the Topographical Branches of the War Office and of the Commander in Chief and the Directorate of Fortifications and Works. They relate to the United Kingdom and overseas.

The maps formerly in WO 38 were added to this series. The series also contains maps and plans formerly in the Public Record Office library and originally from the Quartermaster General's Department, and also material which would otherwise be found amongst the Records of the Ordnance Office and its successors at the War Office (WO).

Detailed descriptions of the records in this series are being converted from The National Archives' paper-based map catalogues. Pieces 1-2501 are currently described in full; detailed descriptions of further pieces will be added to the Catalogue in the coming months.

As far as possible, places depicted on maps or drawings are identified in catalogue descriptions by the names given on, or contemporary with, the documents themselves, although spellings have been modernised and standardised to facilitate searching. Where there has been a significant change to the name of a place or that of the political or geographical area in which it is situated, the current name is usually given in brackets after the name taken from the document. If it has not been possible to identify the place named, the name given on the map or drawing is noted in inverted commas. If no place is named, and the location cannot be identified, this is noted explicitly in the description.

Places now in the London area, but outside the City of London, are identified according to the county or borough in which they were situated at the date when the map or plan was produced. 'London' or 'London:' followed by a borough name, is used in describing material produced during the period of the London County Council (1899-1965) or the Greater London Council and successor authorities (1965 to date). Where appropriate to facilitate searching, the current inner London borough is also noted in brackets. For places which remained in Essex, Middlesex, Surrey and Kent until 1965 only the original county, and not the current outer London borough, is noted.