[Talk-GB] Announcement - OS 1:25k mapping availability for OSM data contributors

Andy Robinson (blackadder-lists) ajrlists at googlemail.com
Tue Oct 6 15:04:26 BST 2009

We are all used to drawing in difficult or far away features by referring to
the NPE 1" to 1 mile out of copyright Ordnance Survey mapping in JOSM or
Potlatch. Its great for long linear features but for accurate stuff, like
field boundaries and detailed information about the landscape, especially in
rural areas, it's not enough.

Enter the OS 1:25,000 scale (two and a half inches to the mile)
1st/Provisional edition [1]. Which I'm happy to announce is starting to make
an appearance for the project.

There are two parts to the availability currently. One focused on providing
it via WMS for use in JOSM and the other as tiles for Potlatch.

The first full sheet (NX88 NW or Dumfries [2]) is available for you to try
out in JOSM [3]. Just add the URL as a custom WMS.

For the Potlatch tiles RichardF has worked up some code magic that should
automate the process of rectification and tiling. It may take me a little
time to get that running and the tiles will probably be served from the new
dev machine which is not quite ready yet so there will be a further
announcement on this.

Both the WMS and google format tiles use the same rectification data.

The time consuming part is manually obtaining the pixel co-ordinates for the
corner gridlines of each sheet (which I have to scan in two halves on my A3
scanner). It has to be done manually to get the best accuracy, which should
be generally 10m once available in Potlatch or JOSM. i.e. significantly
better than was possible with NPE, though note that its still only as good
as the OS originally survey it in the late 19th century. Anyway, it means
that this part is a slow process.

Currently I have around 15% of the published sheets with more arriving every
day. More would be welcome, either by way of donated maps, scans, or funds
to purchase more from retail suppliers (higher cost - usually about £3 to £8
each). With 2027 sheets in the series cost is a factor for how quickly I can
grow the set.

I'll keep the index updated on the wiki with progress (both obtaining and
scanning/tiling) so look out for your area turning up. The majority of the
sheets I have are for England and Wales. Scotland never had full coverage
from this series.



[1] "http://wiki.openstreetmap.org/wiki/Provisional/First_Edition"
[2] "http://osm.org/go/evY0@6R"

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