Pete
For a comprehensive bibliography of OS maps, revisions etc., Richard
Oliver's Ordnance Survey Maps: A Concise Guide For Historians (Pub. the
Charles Close Society for the Study of OS Maps) 1993, reprint with corrs.
1994, will help in 98% of cases. The Survey's history of Lancaster's mapping
from 1845 is covered on p. 99; for Lancashire, equally useful, from 1838 see
p. 148.
Hal Bishop
Archaeology Officer
Torbay Council
01803-207788
-----Original Message-----
From: Iles, Peter [SMTP:[log in to unmask]]
Sent: Wednesday, February 05, 2003 10:18 AM
To: [log in to unmask]
Subject: Re: Digital Historic OS maps - Advice wanted
Digital Historic OS maps - There is a better way than Landmark Ltd
in our
experience, but it might not be classed as 'cheaper', but it depends
on what
you want.
Problems with the Landmark data include
1) that they have cut up and tiled the original sheets to 5km x 5km
squares,
equivalent to the 1:10,000 'quarter sheets' and on any one of these
tiles
you may have sections of one, two or four original maps with
different
publication and survey dates - it also make referencing back to the
original
map a real pain.
2) They have also been scanned from the OS holdings of these maps,
WHICH ARE
NOT NECESSARILY THE FIRST VERSION OF THE MAPS PRODUCED AND MAY BE
REVISED
MAPS PRODUCED 20-40 YEARS AFTER THE QUOTED 'PUBLICATION' DATE.
Sorry to
shout there but I've tried to get them to acknowledge this problem
on their
'oldmaps' web site and to let people know about this - it can be
very
misleading. The changes to the maps were generally things like
railways and
properties immediately adjacent to the Rwy such as mills, but I have
also
found other changes but the important point is that it is not
usually noted
on the map that it is a revised version. To look at this try their
'oldmaps'
site and look at Lancaster city centre and then compare it with the
same
area on our website http://mario.lancashire.gov.uk which is a
web-based GIS
and has the 'real' first ed. 1:10,560 and some 1:2,500 maps on it -
you will
spot a number of extra railways built in the 1850's on the 'oldmaps'
image,
even though they claim a publication date of 1848! They claim that
as this
date is on the map, then that is they date they should quote,
despite it
being 'wrong'. The revised maps are referred to as 'first state',
'second
state', etc. and as far as I know, no one has produced a
comprehensive
bibliography of these - please let me know if you know different.
3) The image quality is very variable, in some places they are
unreadably
black, in others so light that most lines have dropped out
4) They are only available as monochrome images.
5) The licence agreement is very restrictive
Solutions - don't buy from Landmark, digitise your own!
We borrowed a set of the 1:10,560 first edition sheets and a
selection of
1:2,500 first edition sheets (in batches) from our County Record
Office,
carefully selecting the cleanest copy and checking for the revision
problem
mentioned above and asked a commercial company to scan them and
rectify them
to the modern OS grid for us. They were then supplied as 400dpi
monochrome
images (TIF) and 200dpi greyscale images (JPG) on CD-Rom with the
appropriate GIS world files. Cost was £90 per sheet, but they would
produce
the mono-only sheets for £60. You could get them scanned a lot
cheaper than
this, it is the processing and rectification that takes time and
money, but
if you have the time/equipment/software you can do it yourself -
Erdas
Imagine is the software of choice for this but it's not a trivial
job. As
far as we understand the digital maps are then your copyright, to
use/distribute/display/sell as you want.
If you want the name of the firm that did our maps, or to chat about
it
more, email me on [log in to unmask]
Pete Iles, Lancs SMR
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