[OSM-talk] Tagging, map-features and rendering

[Steve Chilton]

Recent posts from Jo and Andy just highlight the inherent problems with
a cooperative venture such as OSM. By its open nature participants are
encouraged to explore whatever route forward takes their fancy (and
suits their skills/inclination).

I started off thinking that creation of suitable data was a simple task
of getting out and doing it. How wrong can you be.
Having explored the existing data, and in particular investigating which
method of editing and outputting to use (initially for proofing
purposes), I have come to a better understanding of the problems the
project is setting itself.

I naively started using the import GPS traces through OSM interface
route, but soon got frustrated by the wait for file to be validated and
appear for editing (pure impatience to get on with the task, having done
some surveying I wanted to get on with the next phase). Then I moved to
uploading via the excellent JOSM interface. My first surveys were
circular bike rides that didn't cross over, re-trace, or doing anything
else complicated. So, using the JOSM option to NOT open as raw data
seemed the way forward - as it joined up the data to segments
automatically. Incidentally, when you do import as raw data I find the
data points very small in the editor. Have I missed something or can you
re-size these to suit (as you can with nodes in the applet)? Then I did
a small test survey of local roads near home, producing more complicated
data points. Subsequent investigation shows that the autojoin now
produces multiple paths, spurs, segments not in order that they were
mapped in (important for rendering textpaths with Etienne's excellent
Osmarender), etc. So, back to entering raw data and compiling the line
segments in the editor (tagging as I go).

I started tagging using class=xxxx as that was what the applet's
drop-down menus seemed to be leading me towards. However, when I
discovered the Map Features page in the wiki and saw the first output
from Nick's development renderer and Osmarender I realised this might
need a re-think. Having scanned the osm-map-features and osmarender
files I have now fixed on a subset of features that are recognised by
this system of outputting. Seeing the ouput in SVG format gives you
clues about tagging and compilation inconsistencies. I have gone back to
the local data that I have collected and re-ordered segments [usually by
deleting and replacing the segments as the applet's re-order segments
tool is not intuitive to use (to me)].

Enough of these ramblings and let's get positive. I today obtained my
Garmin bike handlebar holder and am raring to get out some
evenings/weekends and map more of the local area (Enfield in North
London). Howvere, can I suggest that some information is put on wiki
pages that highlights "tagging" matters? Once any responses to this note
have been assessed I am happy to have a bash at writing that page. And
also that an "Outputs" page be compiled - preferably with major input
from the various renderer developers - explaining what they pickup on
(ways, segments, class, highway, etc), what needs to be considered when
compiling data, and what external routes onwards there are (eg SVG to
PNG, SVG to Inkscape). I don't feel particularly competent to do that
task. There is already an Osmarender page, but it could use summary of
what the tool picks up on so folks are aware (forewarned is forearmed).
Incidentally, reading Jo's mail I would vote for option 3 to auto change
class= tags to highway= tags (sorry maybe that should read ADD rather
than replace), and suggest that the idea of "core attributes" be
propagated strongly amongst contributors to make data as usable as
possible. Anyone who objects to this needs to shout out as to why they
have reason to keep their class data (Nick's renderer?).

Whilst discussions are rightly going on about Foundation, copyright,
data sources, appropriate development paths, etc it is important that
the foundation (the data itself) is solid. By that I mean accurately
compiled, relevantly tagged and accessible data.

[Osmarender hint: if you use the highway=residential tag the 40%
startOffset placement for the road name will invariably throw the name
off or truncate it because these roads are often very short. Editing the
file (in 2 places) to a more suitable number like 20% helps a lot]

Cheers
STEVE

Steve Chilton, Learning Support Fellow
Learning and Technical Support Unit Manager
School of Health and Social Sciences
Middlesex University
phone/fax: 020 8411 5355
email: steve8 at mdx.ac.uk

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