Maps: Ordnance Survey
The CAO holds O.S. maps in the following scales for Brecknockshire, Radnorshire and Montgomeryshire. No edition is complete in its coverage for all these counties, but a comprehensive index is available in the search room.
1": Mile: First edition from the 1830s, revised in the 1870s, incomplete coverage. The sheet numbers for Powys are 42-60.. The later series c1880s to 1912 is likewise incomplete, the sheet numbers for Powys are 151-232.
2": Mile: Photocopies from the National Library of Wales of the first edition working drawings from 1809 to 1836 the full set exists.
6" : Mile: The First edition from the 1880s (very few examples). Second editions from the early 1900s (good coverage). Provisional editions based on the second edition, but with revisions in 1938 and 1948/49 (fair coverage). The numbered series are sub-divided into NW, NE, SW and SE sheets.
25" : Mile: First editions of 1887 are very few. The second editions of the early 1900's form the major part of this collection, including those used for land valuation purposes. Coverage of Brecknockshire is patchy, there is better coverage of Radnorshire and Montgomeryshire, but still many are at present missing.