Ordnance Survey maps date from the early to mid-19th century. Certain scales were revised at regular intervals, thus providing a record of site uses and changes 
in site uses, over time. The scales of most interest to contaminated land are 1:2500 (County Series and National Grid); 1:10560 (County Series) and 1:10 000 
(National grid). The number of editions varies with the part of the country and amount of change that occurred in an area.  
The OS now has digital versions of maps that are updated continuously. Map editions, which provide a snapshot of land use at a particular date, or more accurately 
over a range of dates, are not available for the 1990s/2000s. It is not known whether pseudo editions might be available on request in the future.  
OS maps can be viewed in county libraries or bought from the map shop.