[Tagging] [OSM-talk] Sourced from somewhere it shouldn't have been

Andy Robinson (blackadder-lists) ajrlists at googlemail.com
Thu Nov 5 14:54:49 GMT 2009


Morten Kjeldgaard [mailto:mok at bioxray.au.dk] wrote:
>Sent: 05 November 2009 1:15 PM
>To: Andy Robinson (blackadder-lists)
>Cc: 'Tag discussion,strategy and related tools'; talk at openstreetmap.org
>Subject: Re: [OSM-talk] [Tagging] Sourced from somewhere it shouldn't have
>been
>
>Andy Robinson (blackadder-lists) wrote:
>
>> You can find npe and 7th series 1 inch mapping plus 1:25,000 (2.5 inch to
>> the mile) 1st series on the dev server at:
>>
>> http://ooc.openstreetmap.org
>>
>> The default view is NPE, switch to the others using the layer selector.
>All
>> three layers are available as a backcloth in Potlatch. And with some
>fixing,
>> hopefully all in JOSM soon.
>
>Impressive! You Brits are lucky :-)
>
>Just out of curiousity: how accurate are those pre-satellite-age maps
>compared to the GPS-surveyed maps of OSM?

For the older 1" maps the error can be quite high because the printing of
the gridlines (which is used for rectification) was poor. The later 7th
series will undoubtedly be better. For the 1:25,000 scale the printing of
gridlines is very accurate so that principally leaves the errors that have
always been present in the reference frame, which can be as much as 5m but
generally not worse that that.

Cheers

Andy 






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