[OSM-talk-ie] Tagging townlands in OSM-Ireland

Patrick Casey pcasey at compuserve.com
Fri Sep 12 19:55:12 BST 2008


Hi Kevin,

The flooding of lakes could indeed muddy the waters (excuse the pun).
Indeed, in the porous limestone areas in the West of Ireland where the
turloughs disappear completely or almost completely for part of the year and
then reappear in the wet season when the water table rises the mapping is
presumably a hit or miss business which depends on when the satellite flew
over.

You mention the Ireland page in the Wiki. Where is that ? I found pages for
every other country from Afghanistan to Zululand but none for Ireland.

Paddy


-----Original Message-----
From: talk-ie-bounces at openstreetmap.org
[mailto:talk-ie-bounces at openstreetmap.org] On Behalf Of Kevin Ryan
Sent: 11 September 2008 00:44
To: Discussion of Open Streetmap in Ireland
Subject: Re: [OSM-talk-ie] Tagging townlands in OSM-Ireland


 
Hi Paddy,

I found the same about the place names in the Shannon region (Rineanna was
in the Shannon estuary) and I've moved some of them.  I was worried at
first, being a newbie, but I eventually got fed up with things being wrong
and just fixed them.

The lakes in my area seem to have been drawn from the Yahoo images - and I'm
guessing that the photos were taken late winter or early spring, as one of
them in particular was particularly large - I'm guessing it was in flood -
as it would have been covering the road and railway track.  These I've
generally realigned slightly when as I've done the roads in the area.

Maybe we should have some way of handling lakes when they flood the railway
tracks - then again, maybe CIE should have a way of handling railway tracks
when lakes flood, but that's a different days work...

Thanks for raising the townland question.  Perhaps a section on the
"Ireland" page on the wiki about them might help us to get the ducks in
line.

Cheers,

Kevin.

2008/9/10 Dermot McNally <dermotm at gmail.com>

> Hi Paddy,
>
> Paul has covered pretty much all the points, I think, but just in case...
>
> 2008/9/10 Patrick Casey <pcasey at compuserve.com>:
>
> > I now understand why one or two places in 'my' area in the
> > Tubber-Ruan-Crusheen triangle aren't where they should be on the map
> (e.g.
> > the village of Ruan). May I take the liberty of moving them a few
hundred
> > yards to their correct sites  or does a committee have to vet changes.
> I'm
> > new to OSM and not yet sure of the protocol and the last thing I want to
> do
> > is contravene some existing convention or practice. I'm very conscious
of
> > the fact that in a project like this the participants need to conform to
> > standards to prevent anarchy. Anything else and the OSM becomes useless.
>
> I'll emphasise two things here - firstly, OSM is in every real sense
> an anarchy. Consider the fact that anybody can map and tag anything in
> any way they choose. Though it's certainly true that norms of
> behaviour are important enough that most mappers will go along with
> consensus (like agreement on how to tag townlands, with a view to a
> useful treatment on rendered maps).
>
> Secondly, you should absolutely move stuff you know to be misplaced,
> in particular place nodes. I should have added to my first name that
> the GNS data source is pretty inaccurate, so my import was conducted
> with the expectation of cleanup by those who knew better. However, you
> should be mindful of the fact that some data sources will disagree,
> based on reasons like the following:
>
> GPS inherent tolerances
> Yahoo and Landsat imagery never calculated perfectly (Yahoo generally
> OK, Landsat terrible)
> Mapping slip-ups.
>
> So in cases where there's a chance that the other mapper knows
> something you don't, it can be worth talking before you edit. But
> clearly your case is a clear-cut one.
>
> > If I interpret your tenor correctly there would be no objection if I
were
> to
> > "re-baptise" e.g. Coolbane as a locality. I would restrict such changes
> to
> > places that I know well and have walked over and can vouch for the fact
> that
> > they consist of a few scattered houses or farms or cabhals and not tiny
> > groups of habitations that one might call a hamlet. Would that be OK ?
>
> I absolutely encourage you in this. As I said, I took this approach in
> the NI import based on the experience of the RoI one.
>
> > Some of the lakes in 'my' area seem to have been very roughly drawn (or
> my
> > GPS was faulty). For example, the footpath to Dromore Castle from the
car
> > park (which I walked with the GPS) appears to cross part of the lake.
> There
> > is a New Testament example of walking on water but I haven't yet managed
> to
> > emulate it. Is it possible that those lakes were traced from a
relatively
> > low-resolution satellite image ? I'm talking about small errors here,
> e.g. a
> > couple of hundred yards.
>
> This is expected, and while it's worth correcting the lakes, it may be
> worth thinking about the best method of correction:
>
> Most Irish lakes have been auto-traced from aerial imagery, mostly
> landsat satellite imagery in fact. Landsat calibration with real life
> is poor enough to place lakeside roads under water, but useful enough
> to trace first and move as opportunity presents. I've always had the
> sense that it can be off by as much as 100m. What this means is that,
> where your local lake has a rough outline and is poorly aligned, its
> shape may very possibly be fairly good. This being so, it may be
> better to move the entire lake based on local measurements rather than
> (or rather, before) just editing your nearby bank (since that will
> require similar surgery all around the lake's edge). Moving the whole
> lake can be easily accomplished using JOSM (and probably fairly easily
> in Potlatch too). In JOSM, where there are accurately surveyed roads,
> it's sometimes even possible to adjust such traced lakes by first
> calibrating the landsat image in your editor - as long as you can see
> the roads, you can usually line it up. Then you can move the lake
> without even resorting to your own measurements.
>
> Obviously, if you are willing or able to walk the perimeter of a lake,
> that works too.
>
> > I couldn't understand your statement ".....it's a bad idea to tag for
the
> > renderer....".  Could you clarify that, please ?
>
> It's a kind of motto at OSM. An often-quoted example is that of
> Americans, who may be used to paper maps that display freeways in
> orange. Nonetheless, they shouldn't tag them as secondary roads, which
> just happen on the UK-written OSM renderers to be shown in orange.
> They should instead tag them as motorways and perhaps produce a
> localised renderer if the colour scheme annoys them.
>
> And now, the begging :)
>
> I know that the area you named is entirely on the wrong end of Clare.
> That said, one of the very few OSM gaps in the national road network
> is on the Kilrush end of the N68. I don't suppose you ever drive that
> way with a GPS logger switched on? Traces or actual mapping would be
> extremely useful. Even those parts of the road that are mapped are, in
> places, traced from calibrated Landsat, so a resurvey is overdue.
>
> Happy mapping!
> Dermot
>
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