Welsh maps on-line at National Library of Scotland

[Stuart P]

Now on-line at http://maps.nls.uk

Ordnance Survey, full coverage of England, Wales & Isle of Man at 6" to 1 mile, 1842-1952 - 37,930 sheets [6" to 1mile]
Ordnance Survey, 1:25,000 maps of Great Britain - 1937-1961 - 2,027 sheets [~2½" to 1 mile]
Ordnance Survey Revised new series, England and Wales, 1892-1908 - 691 sheets [1" to 1mile]
Ordnance Survey New Popular edition, England and Wales, 1945-1947 - 114 sheets [1" to 1mile]
Ordnance Survey Seventh Series, Great Britain, 1952-1961 - 190 sheets [1" to 1mile]
Ordnance Survey "ten mile" Planning Maps of the United Kingdom, 1944-1960
Ordnance Survey Five feet to the mile, London, 1893-1896 - 753 sheets