[Talk-GB] OS VectorMap District road files for Devon and Cornwall

[Richard Fairhurst]

Hi all,

In order to assist remapping in the South-West, I've uploaded a bunch of 
OS-derived shapefiles each containing all the roads in a 10km x 10km 
area. You can use Potlatch 2 to bring these geometries into the map, 
saving tracing work.

To load:

1. Open Potlatch 2 at the required area.
2. Click 'Background' -> 'Vector file...'.
3. In the text box at the bottom, paste a URL of the form:
	http://richard.dev.openstreetmap.org/os/SS20_Road.shp
4. Untick 'Simplify paths' and make sure 'Shapefile' and 'Lat/long' are 
selected.
5. Click 'Load'.
6. When the newly loaded layer appears in the table above, change the 
style from 'Potlatch' to 'GPS' (more visible)
7. Close the dialogue

Then, to bring a road through, just alt-click it. You will (obviously) 
need to edit the tags (use Advanced mode) and add connections with other 
roads (the J key is good for this).

Each 10km x 10km square is a different shapefile. To find the URL, go to:
	http://geowiki.com/os.cgi
and type the placename, then just copy and paste the URL it suggests.

I've uploaded road shapefiles for the SS, SW and SX grid areas. If you 
would like a different area or another layer (e.g. rivers), let me know, 
though it might take a while. Alternatively, I've provided instructions 
at the bottom as to how to do it yourself.

There is lots that could be improved about this workflow: implementing 
TagTransform to remap tags automatically, zipping up shape-files, 
allowing Ctrl with alt-click, automatically joining streets, etc. I'm 
very very unlikely to have much time to do this before 1st April, so 
with the best will in the world, it's not worth making "this would be 
easier if..." suggestions unless they're really astonishingly simple - 
sorry. More P2 coders always welcome. :)

This is provided as a service for remapping only. It will on balance 
improve the quality of the mapping in the South-West, but is obviously 
not as good as survey. Some notes on the data:

- VMD has downsampled road geometries which are of a better standard 
than the NPE-traced mapping in large parts of the South-West, but are 
not as good as the best OSM work.
- VMD roads are broken at every junction. This makes them more suitable 
for country lanes than town mapping. Also, some very dense areas (e.g. 
Plymouth) are probably still too large for P2 to manage sensibly. (Plus, 
in my experience, dev.osm.org is not great at serving huge files.)
- Names are only present for 'Minor Roads' and upwards, _not_ for 'Local 
Streets'.
- VMD is subject to the usual OS OpenData licence.

cheers
Richard





== How to create the shapefiles yourself ==

We need to split the shapefiles into 10km x 10km 'tiles' as 100km x 
100km boggles P2 in busy areas.

Download the 100km x 100km VMD shapefiles from the OS OpenData website. 
Make sure you have gdal/ogr2ogr installed. Then, create each 10km x 10km 
tile like this:

ogr2ogr -clipsrc 290000 90000 299999 99999 -s_srs EPSG:27700 -t_srs 
EPSG:4326 -skipfailures SX99_Road.shp SX_Road.shp

In other words: "clip to this bounding box, reproject from OSGB to 
lat/long, write to SX99_Road.shp, read from SX_road.shp". (Yes, ogr2ogr 
does take destination and source files the wrong way round.) You can 
fairly trivially put a loop around this to produce all 100 tiles.

Upload the resulting .shp, .shx and .dbf to your webspace. (P2 doesn't 
read .prj files so you can ignore those.) Put a crossdomain.xml at the 
root of it (you can copy the one from 
http://richard.dev.openstreetmap.org/crossdomain.xml) to tell Flash that 
yes, it is allowed to read files from there.