Re: [Talk-GB] OS 1:25K tracing

[Steve Hill]

On Fri, 22 Jan 2010, Jason Cunningham wrote:

> We can't trace over google/bing satelite imagery because contract/terms of
> use, but it is tempting use the google satellite images to check what can be
> traced from the 1:25K (still the chance google is out-of-date!). This
> doesn't appear to go against google's terms of use.

Yes, I don't see a problem with this, but it would be nice to hear some 
legal direction from those in the know.

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Re: [Talk-GB] OS 1:25K tracing

[Steve Hill]

On Fri, 22 Jan 2010, Dave F. wrote:

> I wouldn't even rely on 'solid' entities such as rivers & streams.
> I've got three in my area that have either meandered naturally, or been 
> diverted by man. One being a major civil engineering job to prevent a river 
> undermining a railway line.

I've been tracing the high and low water marks from the 1:25K maps (I 
guess these can change significantly, but its still probably a lot more 
accurate than what we have already - surveying the tidal extents is 
pretty difficult) and have found it quite interesting how much the 
position of some of the rivers have naturally changed over the years.  Not 
just changes to where they flow over a beach, but sometimes quite 
significant changes to where they flow over "solid ground" just before 
they get to the beach.

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[Talk-GB] OS 1:25K tracing

[Steve Hill]

Since the out of copyright 1:25K maps appeared, there has been rather a 
lot of tracing going on.  On the whole, I think the availability of this 
data is good.  However, I have noticed that around the Gower peninsula, 
quite a few nonexistent roads, etc. have appeared and have been attributed 
to these maps.

I'd like to take the opportunity to point out that blindly tracing fairly 
old maps without doing any kind of a survey is pretty counterproductive - 
someone now has to go around and survey and delete these bogus features.

By all means, trace the maps to add stuff you know is there, but please 
don't just trace everything without some local knowledge.

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[Talk-GB] FreeMaps petition

[Steve Hill]

Oh dear, is it me or have the government managed to *completely* miss the 
point: http://www.number10.gov.uk/Page20555

Shame the petitions website doesn't provide any sensible method to respond 
to the government's response and open a dialogue with them.

-- 

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Re: [Talk-GB] Sand Bar

[Steve Hill]

On Wed, 5 Aug 2009, Peter Childs wrote:

> How to I tag a Sand Bar that extends 50meters in the sea at low tide
> and disappears at High Tide. Its called "The Street" and its in
> Tankerton, Kent. Uk
> http://www.openstreetmap.org/?minlon=0.2519539&minlat=51.2615685&maxlon=0.6075064&maxlat=51.5630983&box=yes

What I have tended to do around the beaches of Gower is to mark the 
non-tidal bit of the beach and the tidal bit as separate polygons, setting 
a "waterway=tidal" tag on the tidal bit.

e.g. http://osm.org/go/euMTH1gJ--?layers=B000FTTT

The Worm's Head tidal causeway is the same:
http://osm.org/go/euG5vJYH-?layers=B000FTTT

Of course, it currently renders as beach, so some tweaks to the Mapnik 
template might be nice.

> Is there some way to place brake waters, onto the map, (ie wooden
> structures that stop the sand/pebbles moving down the beech)

http://wiki.openstreetmap.org/wiki/Harbour suggests man_made=breakwater
Also see http://wiki.openstreetmap.org/wiki/Proposed_features/Breakwater

  - Steve
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Re: [Talk-GB] Roundabout, ways and relationship policies

[Steve Hill]

On Fri, 24 Jul 2009, Jack Stringer wrote:

> I am not a bus spotter or a photter but why would I want to know what
> route the 172 Bus takes? Other than from a route planning PoV so that
> I don't get stuck behind them all the time.

Well, that's one example.  How about other things like researching where 
to live so you're not on a bus route (if you don't like the sound of 
busses trundling past your window all day).  I'm sure there are many 
examples I can't think of, but it seems to me that putting accurate data 
in OSM is a Good Thing.

> I understand that people would like to put bus routes into OSM but
> does it have to require the cutting up of roundabouts and junctions?

I don't really see what the big deal is with cutting stuff up - it 
shouldn't cause any problems, if it does then it is the tools that need to 
be fixed rather than kludging the data to work around flaws in the tools.

In the long run, I think we'll move away from tagging ways and just tag 
relations.  That way, updating the tags on a road wouldn't involve 
updating the same tag on each way that makes up the road - you'd just 
update the relation.  Similarly, updating the tags on a bus route wouldn't 
involve finding all the ways that make up the bus route, you'd just update 
the relation.  We're not at that stage yet, but I don't see a good reason 
for reversing the progress we've already made in that direction.

  - Steve
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Re: [Talk-GB] Roundabout, ways and relationship policies

[Steve Hill]

On Thu, 23 Jul 2009, Jack Stringer wrote:

> Why do we cut them up for the bus routes? Wouldn't it be easier to build a
> navagation app at does the calculation using all the stops as waypoints.

The resulting calculated route might not actually match the route the bus 
really takes.  You might argue that it doesn't matter so long as the bus 
goes via all the stops, but IMHO it is wrong since there may be reasons 
for knowing the route the bus actually takes rather than just what stops 
it goes via.

> Wile I have been learning to map I hate it when I have load of short ways
> (few meters to a few hundred meters). I think it looks crap I often end up
> deleting what I have done then re-drawing it.

The rendering of a way that has been chopped up should be much the same as 
one that hasn't.  I suspect things like the name of the way might be 
repeated too frequently if it is cut up, but that's something that should 
be fixed by the data user (e.g. at the osm2pgsql stage for Mapnik 
rendering) rather than flaws with the renderers restricting how data is 
represented in the backend.

> KIS (Keep It Simple) is a very handy engineering term.

Unfortunately one person's simple is another's complicated. :)

  - Steve
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Re: [Talk-GB] Roundabout, ways and relationship policies

[Steve Hill]

On Thu, 23 Jul 2009, Greg Stark wrote:

> Fwiw even (1) isn't necessarily true. The Magic Roundabout famously
> has a counter-clockwise loop in the centre. And there are other such
> roundabouts where the central loop isn't even one-way.

I wouldn't really consider the magic roundabout to be a roundabout 
(although others may disagree I guess...  I certainly wouldn't expect a 
satnav to say "take the 4th exit at the roundabout" when approaching the 
magic roundabout :).  It is really a collection of interlinked 
miniroundabouts.

> I do think (5) is kind of important. Critically there are special laws
> dictating right-of-way and rules for navigating roundabouts which
> aren't necessarily the same as for a simple loop of one-way roads.

Not really - the right of way laws for a roundabout are the same as any 
other one way system that consists of a major road with side-roads joining 
it (i.e. you give way to the traffic already on the major road).  I guess 
things get fuzzier as the roundabouts become smaller and the "give way to 
the right" rule starts talking about traffic that is still on the side 
road to the right instead of actually on the roundabout.

> I have to say I find it awfully annoying to edit ways in an area where
> every path is broken up into ten million single segment paths because
> there are bridges, tunnels, surface changes, hazards, etc. It would be
> awfully nice to have one reasonably big way and then shorter ways
> marking the exceptions.

IMHO this could be better done with relations and improvements to the 
editors.

  - Steve
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Re: [Talk-GB] Roundabout, ways and relationship policies

[Steve Hill]

On Thu, 23 Jul 2009, Donald Allwright wrote:

>> http://www.openstreetmap.org/?lat=52.936219&lon=-1.24996&zoom=18&layers=B000FTF
>
> How about this one:
> 
>
> which fulfills all of the above 5 criteria, but just has a 'short-cut' 
> across one side. In this case, each 'junction' on the roundabout is 
> controlled by traffic lights and has between 2 and 5 lanes. I have to 
> navigate it frequently and I can't say it's one of my favourite ones!

These aren't too dissimilar.  Although I'm curious how your example works 
- it looks like the "short cut" is only of use for people who have come 
off the southbound carrigeway of the motorway and want to get back on the 
southbound carriageway - why wouldn't they just go along the motorway 
instead of taking the junction?  (I presume I'm missing something 
important about who can use the shortcut lane :)

  - Steve
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Re: [Talk-GB] Roundabout, ways and relationship policies

[Steve Hill]

On Thu, 23 Jul 2009, Andy Allan wrote:

> I disagree - I've come across town-centre one-way systems that are
> smaller than some large out-of-town roundabouts. There is a clear
> distinction between them in the way they are signed  - e.g. using a
> "roundabout ahead" warning triangle, so we should in fact record which
> are roundabouts and which are just circular oneway streets, since they
> are in fact different on the ground.

Ok, that's a fair point.

Of course, all the warning signs should be on the map too :)  (No, I'm not 
seriously expecting this to happen)

I'm just trying to think what makes a roundabout a roundabout instead of 
just a one-way system.  So far I've come up with:

1. It is one way in the appropriate direction (clockwise in the UK)
2. All the roads leave/join the outside of the loop (*)
3. It generally isn't very built-up in the middle (**)
4. It has a reasonably circular shape (***)
5. It is signposted as such

Of course, there are sadly lots of exceptions...

* Increasingly there are roundabouts with roads running through the 
middle:
http://www.openstreetmap.org/?lat=52.936219&lon=-1.24996&zoom=18&layers=B000FTF
The road through the middle is generally one-way though, and usually just 
one road.

** 
http://www.openstreetmap.org/?lat=50.910579&lon=-1.400756&zoom=18&layers=B000FTF
(The Charlot Place roundabout in Southampton now has the reasonably tall 
Jury's Inn hotel in the middle of it - I'm sure people can think of many 
others)

*** Can't think of any oddly shaped roundabouts off the top of my head, 
but I'm pretty certain that there are plenty. :)

  - Steve
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Re: [Talk-GB] Roundabout, ways and relationship policies

[Steve Hill]

On Wed, 22 Jul 2009, Nicholas Barnes wrote:

> Should, for example, the component ways making up the roundabout be
> grouped in their own "I'm a roundabout" relationship?

Do we need to be able to tell which ways are part of a roundabout anyway? 
I mean, on the ground a roundabout is just a one-way circular road with 
some other roads coming off it - there isn't really anything special about 
it that makes it a roundabout.

The only use of an explicit "I'm a roundabout" tag/relation that I can 
immediately think of is to make driving directions more human-readable 
(i.e. "At roundabout, take the 3rd exit").  In this case it may be better 
for the data user to use some heuristic, much as we do ourselves when we 
look at a piece of road.  e.g. If there is a closed (clockwise in 
the UK) one-way loop with a diameter of less than X metres then consider 
it a roundabout when generating human-readable driving directions.

Using this kind of heuristic would also have the advantage of setting an 
application-specific upper bound to the size of a roundabout - when 
roundabouts get beyond a certain size then it is probably better for 
sat-navs to go back to the usual "take the next left" driving directions 
instead of "take the 7th exit".

  - Steve
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Re: [Talk-GB] Reverting all Liam123's edits

[Steve Hill]

On Tue, 21 Jul 2009, Chris Fleming wrote:

> It's also worth noting that if we ban him he may just go and open a new
> account and continue... at least now we know what to keep an eye on.

This is true.  But it might also draw his attention to the problem and be 
the end of the matter.

Some thoughts on sensible protections which could be implemented in the 
future:
1. The ability to ban a user from editing.
2. The ability to ban an IP address or range of IP addresses from editing 
(this is extreme).
3. The ability to ban user creation from an IP address or range of IP 
addresses.

At least (2) and (3) need to be time limited - we can't really justify 
banning indefinately based on IP address.  And of course, any kind of ban 
is a pretty extreme act so needs some kind of consensus that it is the 
right course of action.

I also agree that it would be nice to be able to monitor an area for edits 
from "untrusted" users so that both new users and vandals can be quickly 
spotted (vandals so that their acts can be monitored and reverted as 
appropriate, new users so that they can be helped).

  - Steve
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Re: [Talk-GB] Reverting all Liam123's edits

[Steve Hill]

On Tue, 21 Jul 2009, David Earl wrote:

> He keeps coming back, day after day, making nonsense edits, but not in a
> random way. It's not just scribbling.

(Disclaimer: I've not done any work in the areas affected, haven't looked 
at the user's edits and so have no specific opinion on whether the user is 
in the wrong or not).

If there is a user who (by general consensus) is making nonsense edits and 
is continuing to do so after having been taken to task by email, I would 
have thought the first thing to do is to ban the user from making edits 
before considering what to do about the edits they have already made. 
Bonus points for being able to display a message explaining *why* they've 
been banned when they next try to edit stuff, with details of who to 
contact to resolve the situation.

If you just revert all the user's edits without doing something about the 
ongoing problem, you're just going to end up with a whole load of more 
edits that need reverting in the future.

  - Steve
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Re: [Talk-GB] printing from website

[Steve Hill]

On Sun, 12 Jul 2009, Jack Stringer wrote:

> Something that tells you that trick.

I'm not sure that clicking on your browser's "print" button in order to 
print the thing you're currently looking at in the browser qualifies as a 
"trick" does it?  Seems like SOP for anyone using a computer to me?

  - Steve
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Re: [Talk-GB] Amenity Editing

[Steve Hill]

On Fri, 3 Jul 2009, Jack Stringer wrote:

> Going by that theory how do you post code 2 farms that are 1mile appart but
> have the same postcode and are on different roads?

Tag both roads with the same postcode?

> that set out to remove the extra data (scripted) and put in the ways but for
> now we just need the postcodes.

Good luck with that - *every* time I have suggested trying to migrate 
existing data from depricated tags to their replacements (either by 
scripting or manually), I've been shot down in flames.

> I could take you arround a local town that has some
> very interesting ways to number houses.

House numbers are not at issue here - clearly they must belong to the 
building itself.  The point I was raising was that your address tags 
contained a lot of data that was shared amoungst many buildings.

  - Steve
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Re: [Talk-GB] Amenity Editing

[Steve Hill]

On Fri, 3 Jul 2009, WessexMario wrote:

> A lowest level postcode (SN13_2PQ) is not unique for a node, as multiple
> dwellings will have the same postcode, so this leads to having multiple
> tags for what is essentially a single data item, a postcoded area of land.

It should be unique to a way (or part of a way) though.

> Marking postcodes on a way could be problematic, as there can be
> different postcodes on opposite sides of a road.

Really?  I've not come across that - if a street has more than one 
post code, doesn't it just get split along its length?

If you really do get different post codes on opposite sides, you could 
have a postcode:left and postcode:right type pair of tags though.

  - Steve
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Re: [Talk-GB] Amenity Editing

[Steve Hill]

On Thu, 2 Jul 2009, Jack Stringer wrote:

>> There is also an issue of keeping the data up to date - having loads of data
>> in OSM is great, but we run the risk of it going stale if we're not careful.
>
> In that case you might as well let Google win the war when it comes to
> maps with data on them. Like I said before with such a large userbase
> we should be able to update and fix errors much quicker than Google
> and other routing programs.

I'm not saying "we don't want lots of data", I'm just raising it as a 
potential issue to be discussed.  There may be potential workarounds (for 
example, flagging old data on the rendered map so that people can 
periodically recheck it, etc.).

> By putting the Postcode in we are supply OSM with the postcode to be
> able to give that street a post code, same goes for streets.

Rather than having the postcode in a separate "addr:postcode" tag for each 
building on the street, I would think it would be better to tag the street 
itself with the postcode and then somehow link the buildings with the 
street (relations?)

> For example I want to find a pub called 'The
> King's Head' I can seach for them by country, by City.

This is more or less the same problem as street names - to search for 
"High Street", you need to identify the city that street is in.

> I noticed
> someone say the other day that OSM is about the data not the map. The
> map is a by product of the data. The data that we put in could also be
> used to make a Pub guide, or restaurant guide if people are going to
> have to put in information about a location it maybe worth putting in
> as much as we can find out.

Absolutely - I'm just saying that finding some way of normalising the data 
would be a Good Thing.  There are lots of advantages to having a 
normalised data set, the biggest one I can think of is that if you tag 
much of the addressing information to the street, rather than the 
individual building, then you have automatically provided most of the 
address for *every* building on that street.

  - Steve
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Re: [Talk-GB] Amenity Editing

[Steve Hill]

On Thu, 2 Jul 2009, Jack Stringer wrote:

> Most of this data can be
> found openly on the companies own website so I doubt they will have
> issues with us including the data as they want to be found on the
> maps.

Common sense and intellectual property rarely go together.  The post 
office want everyone to use post codes but are quite restrictive of 
licensing the database.  TV channels want everyone to know what programmes 
they are showing but they are very restrictive over licensing of the TV 
schedules.  Similary, I think you might need to check with the copyright 
holders of this data before including it in OSM.

There is also an issue of keeping the data up to date - having loads of 
data in OSM is great, but we run the risk of it going stale if we're not 
careful.

> addr:street=Bath Road
> addr:city=Bristol
> addr:postcode=BS4 3BD
> addr:country=GB

It seems to me that this data should be derrivable from the map itself. 
Rather than duplicating data by adding addresses and postcodes to each 
business/building, I think it would be better to figure out a good way of 
deciding which street, city and postcode the building is attached to.

  - Steve
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Re: [Talk-GB] Tank=yes?

[Steve Hill]

On Fri, 12 Jun 2009, Bruce Cowan wrote:

> Also, on the A816 between Lochgilphead and Oban, there is a duck warning
> sign [2]. Surely this would be ducks=yes (or indeed hazard=ducks).

Surely ducks=yes should be interpretted like hgv=yes - i.e. ducks are 
allowed to use the road (I'm not aware of any legislation that makes it 
illegal for ducks to walk down roads :)


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Re: [Talk-GB] Speed Limit - Trains Was: Re: maxspeed field - what units should we use. etc

[Steve Hill]

On Fri, 5 Jun 2009, Peter Miller wrote:

> I am certainly not proposing separate ways for separate lines. I think
> there should either be one way for a bunch of parallel tracks or
> alternatively one way per track if people are getting nerdy (surely
> not!).

Tracing individual tracks might make sense if people are tracing from 
photos.  Especially true for sidings, etc.  I don't really see it as much 
different to having separate ways for the two sides of a dual carriageway.

  - Steve
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Re: [Talk-GB] Question regarding mapping inaccuracies.

[Steve Hill]

On Fri, 29 May 2009, Chris Andrew wrote:

> My question is, can we (do we?) automate the
> checking of roads to ensure they are connected to something, and if
> not, is it possible to highlight them, rather like unnamed roads can
> be shown in red?

Having roads which come very close to being connected whilst not actually 
connecting is often a legitimate thing to do - certainly around here there 
are quite a few roads where they almost join but have a footway, a patch 
of grass or some bollards between them.

  - Steve
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Re: [Talk-GB] Sat Navs to stop working?

[Steve Hill]

On Thu, 21 May 2009, Chris Jones wrote:

> And with any luck Galileo should be up and running in a few years...

They are still claiming they will have 30 sats up by the end of 2013... 
assuming that includes the 2 test sats they have in orbit already, they 
are going to have to launch 28 satellites in 4.5 years.  Averaging a new 
satellite every 2 months doesn't seem very likley in the current economic 
climate, sadly.

  - Steve
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Re: [Talk-GB] Ordnance Survey

[Steve Hill]

On Sun, 26 Apr 2009, Shaun McDonald wrote:


It's interesting to see that there is a moderator stating "there have been 
quite a few comments on
here about the availability of administrative boundaries."
I wonder if they will get enough people saying the same thing to change their 
plans.


The comment "As the section above on An extended OS OpenSpace service 
indicates, official boundaries information will form part of this extended 
service." indicates to me that they either don't understand the copyright 
concerns being raised (and think that "making available" data (through 
OpenSpace), rather than making it copyright-free is what people are asking 
for) or they don't care.


 - Steve
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[Talk-GB] OSM mentioned in the Peak BMC newsletter

[Steve Hill]

Thought this might be of interest - looks like OSM (and the cycle map and 
piste map) got a brief mention in the spring British Mountaineering 
Council Peak area newsletter:

https://www.thebmc.co.uk/bmcNews/media/u_content/File/your_bmc/newsletters/Peak%20Area%20Newsletter%20February%202009.pdf

(page 3 - probably shouldn't read too much into that :).


  - Steve
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Re: [Talk-GB] Wincanton streets in the news

[Steve Hill]

On Wed, 8 Apr 2009, Jonathan Bennett wrote:

>> You'd need a different projection since the disc is flat.  :)
>
> Coordinate system, surely?

That too.

North/south/east/west are replaced by hubwards, rimwards, turnwise and 
widdershins.  I guess that your coordinates would measure distance from 
the hub and angle around the hub from a standard datum.

  - Steve
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Re: [Talk-GB] Wincanton streets in the news

[Steve Hill]

On Tue, 7 Apr 2009, Tim Waters (chippy) wrote:

>> Ankh-Morpork (If any one is going to map that I'm not sure where we put 
>> the data :)

You'd need a different projection since the disc is flat.  :)

  - Steve
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Re: [Talk-GB] Yahoo coverage map

[Steve Hill]

On Sun, 5 Apr 2009, Steve Chilton wrote:

> Because I wanted to know, and as an exercise in OpenOverLayerIng, I 
> have produced a map combining the extent of Yahoo aerial imagery 
> coverage in GB with an overlay of the significant places calculated to 
> be in most need of mapwork (from UK_Map_Priorities).

Interesting stuff - it really shows just how limited the aerial coverage 
is though. :(

Do you know if Yahoo are actively expanding their coverage?  It's quite 
surprising to see some large cities like Birmingham not included.



  - Steve
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Re: [Talk-GB] Possibly using "highway=path" for country footpaths

[Steve Hill]

On Fri, 3 Apr 2009, David Earl wrote:

> FWIW, I agree largely with the specific points on your wiki page, but I don't 
> think it will happen because of the effort involved.

The wiki page wasn't really supposed to be a "this is how it needs to be" 
solution - the hope was to get people talking about how stuff can be 
improved without immediately dismissing anything that wasn't on the path 
of least resistance.  I can understand people being indifferent, but to be 
met with sarcastic replies and put-downs instead of intelligent 
conversation was pretty offputting.

Personally, I don't think the current tagging scheme is really 
maintainable in the long run and that eventually there will need to be a 
revolution, rather than evolution, in the way the data is represented, and 
I worry about the future of project if people with new ideas are turned 
away like this.

> There is also a camp which actively 
> wants a node to be able to have more than one "type" in your terminology: we 
> have (non-accidental) examples of place=town and building=town_hall for 
> example, and (worse) place=town and amenity=post_box on the same node. I 
> think that's ludicrous myself, and I'm sure you do too, but there are those 
> who don't see it that way.

I agree that this sounds pretty crazy (although I'm rather of the opinion 
that using a node instead of an area to identify a town for anything other 
than a temporary measure is wrong).  There are a lot of cases where 
tagging objects as multiple things makes sense though - one example was 
given on the wiki page with roads that become pistes in the winter, but 
there are other such examples.  There may even be merit in having a single 
node tagged as both a posting box and a bus stop if it happens to be a 
pole with both a posting box and a bus stop mounted on it.


  - Steve
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Re: [Talk-GB] Possibly using "highway=path" for country footpaths

[Steve Hill]

On Fri, 3 Apr 2009, Ed Loach wrote:

> I'm beginning personally to think that
> highway= were all a mistake and that
> highway=path and designation=public_footpath/etc, along with
> suitable access keys (foot, bicycle, etc) would have been a better
> starting point

I think even that is a bit too high level.  You don't really need to 
specify whether it is a path, road, etc - all we should really care about 
is what sort of traffic can use it (i.e. "motorcar=yes|no|designated", 
etc.)  From this you can easilly work out what *sort* of way it is (i.e. 
if it allows pedestrians and no one else, clearly it is a footway; if it 
allows cars then it is a road, etc).  Any extra attributes are a bonus - 
width, surface, classification (e.g. for roads this might be "motorway", 
"primary", "secondary", etc.).  Similarly, things like whether the road is 
in a residential area should be an extra attribute, not a fundamental 
classification of the way.

However, mistake or not, we have what we have and making fundamental 
changes doesn't seem especially likely (I have in the past made 
suggestions regarding the fundamental data structure and have been met 
with nothing but sarcastic replies and put-downs - I find it quite 
depressing that no one seems interested in even thinking about any 
revolutionary changes instead of just continuing down a potentially 
dead-end route.  See my brain-dump on the wiki: 
http://wiki.openstreetmap.org/wiki/User_talk:Steve_Hill)

  - Steve
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Re: [Talk-GB] Possibly using "highway=path" for country footpaths

[Steve Hill]

On Fri, 3 Apr 2009, David Earl wrote:

> In highway engineering terms in the UK a "footway" is always alongside a
> road, and we don't tend to mark those separately anyway.

This is a slightly separate issue, but not marking them is a bit of a 
problem in some cases because we end up with things like foot bridges 
which are unconnected at both ends because there is no separate footway 
marked along the side of the road.  I'm not really going to comment on 
what the "best practice" is for this case at the moment, just pointing out 
that it can be a problem.

> I just don't see the distinction between a muddy metre wide path that
> happens to run between houses from one that doesn't. And if it is
> surfaced, we have a means to say so already.

I've got to agree with this.  I missed the discussion when the 
highway=path tag was agreed, but I have never really seen the need for it. 
If it is something I can walk along then it's a footway - I don't much 
care whether it is in an urban area or on the top of a cliff in the middle 
of nowhere, none of that changes what I can do on the way (i.e. walk).

> Well, you know my view on this. A cycleway is a cycleway if it is signed
> as a cycleway, not because it appears to be constructed to a standard
> that happens to be suitable for carrying bikes. Likewise bridleway,
> which in the UK permits cyclists to use it (by default).

Also, there's a legal distinction between cycleways and footways to think 
about - it is illegal to cycle on a footway, and similarly if you were 
walking on a designated cycleway I suspect the courts might not look 
at you favourably if you were hit by a bike (especially if there's a 
perfectly good footway following a similar route).  So marking up a way as 
a cycleway just because it _looks_ suitable for bikes is not a sensible 
move.

In some cases a track is both a footway and a cycleway (often with a line 
down the middle to separate the cyclists and pedestrians).  I'm not sure 
of the best way to tag this - do we tag it as a footway with cyclists 
allowed, a cycleway with pedestrians allowed, mark up 2 independent ways 
next to eachother, or something completely different?  (it is a good 
argument for not using the single "highway" tag to describe the legal 
properties of a way, such as "footway" or "cycleway", where it may 
actually be both).

> And where did this arbitrary 2m come from? That would mean some signed
> cycleways in Cambridge wouldn't be marked as such because they are wider
> than 2m. Perhaps you are trying somehow to distinguish between a
> specially constructed cycleway and a road which has been converted for
> cycle use. But in my mind that's just a wider cycleway.

And indeed, people can already use the "width" tag to signify how wide the 
cycleway is - what it was historically used for is not important for most 
renderings of the map.  There may be merrit in marking up the historical 
use through other tags, e.g. something like "highway=cycleway, 
historically:railway=rail" or similar for a disused railway line that is 
now a designated cycleway, but that is another discussion - I don't 
believe what an object used to be should have any real bearing on the 
mainstream tags.

Unless someone can explain to me a really good reason for using "path" 
instead of "footway", I really don't much feel like having to resurvey all 
the footways around here...

  - Steve
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Re: [Talk-GB] Free National Grid Vector Layers for gas and electricity?

[Steve Hill]

On Mon, 16 Mar 2009, Donald Allwright wrote:

> It would seem that being used as a basis for just
> about everything means that no-one else can ever use those data without 
> paying the OS a fee.
> Must be a nice little earner for them. Of course OpenStreetMap imposes 
> similar restrictions,
> except that paying a fee is replaced with the far less onerous requirement 
> for derived works
> to be CC-BY-SA licensed. (Ignoring the issues to do with why we need to 
> change the licence
> for now).

Whether or not the CC-BY-SA requirement is less onerous rather depends on 
what you're doing with the data.

I haven't looked at any OS licence conditions, but I imagine that if you 
derive your data from OS maps, then you can probably combine your data 
with another commercial map so long as you continue paying OS a licence 
fee.  On the other hand, data derived from OSM must be CC-BY-SA and 
combining it with any commercial map would create a derived work which 
would need to be CC-BY-SA - it's unlikely that the commercial map supplier 
is going to allow this.

Also, I suspect that selling maps is a nice little earner for people such 
as the land registry, so licensing them all as CC-BY-SA isn't in their 
interest (as much as it may be in the tax payer's interest).

  - Steve
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Re: [Talk-GB] Efficient processing of map data for rendering (BOINC).

[Steve Hill]

On Fri, 23 Jan 2009, Matt Amos wrote:

> this might be helpful
> http://svn.openstreetmap.org/applications/utils/export/tile_expiry/

Yes, I had a look at that script, but it only expires tiles with nodes on 
them, which I think is rather too simplistic.  The readme says that it is 
unusual for the gap between nodes to be larger than a tile, but in my 
experience this just isn't true at all.

So my idea was to work on the postgis objects themselves during import. 
This should have some advantages:
1. We don't need to duplicate any work in translating OSM objects into the 
objects that are actually rendered - osm2pgsql already does this and we 
don't have to know or care how.
2. We don't need to duplicate work parsing the OSM XML file - this should 
give some speed improvements.
3. There should be a reduced number of database lookups because the only 
extra things we need to look up in the database are the postgis objects 
that are being deleted.

The plan is to have osm2pgsql insert a list of dirty tiles for the maximum 
zoom level into a postgres table.  I wrote a script that goes through each 
zoom level, starting at the maximum and working back to 0.  Each zoom 
level has a minimum age associated with it and when the tile has been 
dirty for that long it is deleted and the coordinates for the tile at 
zoom-1 are inserted into the table.  The idea being that low-zoom tiles 
change more frequently than high-zoom tiles, but are less interesting and 
more effort to render so shouldn't be re-rendered immediately.

>> From my experience, the number crunching doesn't really seem to be the
>> limiting factor - database I/O is the biggest overhead for OpenPisteMap
>> (although that may be partly down to the massive amount of SRTM contours
>> data it has to handle while rendering each tile).
>
> +1
>
> this is one case where one big raid array is much better than many
> distributed disks.

I was wondering if anyone had done any tests on the speed of a database 
that is distributed over a cluster of servers.  I would imagine that there 
would be speed improvements, but I'm not sure what the overhead is like 
for actually working out which server contains the data you're after.

Another possible solution is to have a number of completely independent 
rendering machines with their own copy of the database and just 
round-robin the rendering requests between them.  This is obviously not 
something that could be done with BOINC or similar - not many people would 
want to dedicate 60GB of their hard drive to the OSM postgis database. :) 
But it could be done with a cluster of dedicated servers.

However, I would be really interested to see just how much load there 
would be on the rendering servers if tiles were rendered on-demand only if 
they hadn't been rendered before or if they have really become dirty since 
the last render.  It just may be that there is no need to chuck lots of 
hardware at the problem if tile expiry is done well.

  - Steve
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Re: [Talk-GB] Efficient processing of map data for rendering (BOINC).

[Steve Hill]

On Wed, 21 Jan 2009, Chris Andrew wrote:

> I notice that people often mention the delay in map edits being
> applied and made _live_.

On a related note...

For OpenPisteMap, I apply the diffs to the PostGIS DB every minute, so it 
only lags behind the live data by a few minutes.  However, it doesn't 
currently automatically expire any tiles from the cache, so it won't 
re-render a tile after the data has been changed.

I'm currently working on modifying osm2pgsql to create a list of tiles 
that have been changed as it applies the diffs so that they can be removed 
from the cache (and thus re-rendered on the fly when someone requests 
them).

My initial, very simplistic attempt was rather unsuccessful though - I 
made osm2pgsql calculate bounding boxes around every object being deleted 
or created.  However, for some objects the bounding box can be extremely 
large (especially relations) so it expires a very large number of tiles.

I think my next attempt will involve calculating which tiles a LINESTRING
intersects.  However, I'm not sure what to do about POLYGONs - 
technically, every tile within the polygon should be expired, but that 
could be a potentially huge area.  Maybe the answer is simply to put in 
some sanity checks that ignore polygons that cover massive areas.

> With the OSM community growing by the day, this problem can only get
> bigger.  Does anyone know whether anyone has consider using a
> distributed client [1] such as BOINC [2] to do the _number crunching_?

>From my experience, the number crunching doesn't really seem to be the 
limiting factor - database I/O is the biggest overhead for OpenPisteMap 
(although that may be partly down to the massive amount of SRTM contours 
data it has to handle while rendering each tile).

  - Steve
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Re: [Talk-GB] Mapping the unloved and unwashed

[Steve Hill]

On Tue, 16 Dec 2008, Peter Miller wrote:

> google are saying is that if one places a layer of OS data on top of google 
> data then google don't claim ownership of that data

Is this actually different to the OS's rules?  My take on the OS's 
complaint was that the councils' data was actually derived from the OS 
data, not just overlaid.  i.e. if they want to plot the location of a 
public toilet, they would know that the toilet is on the corner of roads 
A and B, so would use the OS layer to find roads A and B and place their 
marker on the corner.  Thus the "toilets" marker is derived from the OS 
data because they used the OS's data about the roads to geolocate it.  I 
had assumed that if the council actually had lat/lon coordinates for the 
toilets then there would be no licensing problem since they would never 
need to use the OS data to geolocate the marker (even though they may be 
displaying the marker on an OS map for the end-user).

Or have I misinterpretted the OS's complaint?

  - Steve
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Re: [Talk-GB] Mapping the unloved and unwashed

[Steve Hill]

Peter Miller wrote:
> We all know about the OS licencing issues and so do councils! There is 
> a real bun-fight between the OS Google and councils over licencing.
> http://www.guardian.co.uk/technology/2008/nov/20/ordnance-survey-google-maps 
>

Ok, that's pretty interesting - it is good to see that the councils are 
starting to realise how the licences can come back and bite them.  The 
article mentioned that Google has changed their mapping licence to make 
clear that it isn't claiming ownership of the data - does this mean that 
their licence would now allow us to trace their satellite photos?


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Re: [Talk-GB] Mapping the unloved and unwashed

[Steve Hill]

On Fri, 12 Dec 2008, Peter Miller wrote:

> I have been working on adding wiki pages for every County and Unitary
> Authority in the UK (there are 140 in total) so that we have a
> consistent place to add this sort of information. There were articles
> for some and there are about 19 added so far. Could people add county
> pages for their areas and and use this for a hit-list section of
> wanted places?:
> http://wiki.openstreetmap.org/wiki/Category:County_in_England

Just a thought, but UK != England - might it be an idea to rename this 
page, or is the plan to create separate pages for Wales, Scotland, 
Northern Ireland...?

> Do remember that the local councils might be interested themselves.
> There is growing official awareness that OSM exists and might be
> useful to them. That is one reason why I am building the local
> authority pages.

I'm not sure why the councils would use OSM - as far as I know the 
councils' internal systems (e.g. highways department, etc) are heavilly 
based on OS maps with the council's own layers overlaid.  This means (as I 
interpret it):

1. The council's own layers are derived from OS maps so could never be 
integrated with OSM
2. Since the councils have to publish their maps they presumably already 
have a licence from OS to do so, so using OSM *as well* won't save them 
money.
3. Like it or not, OS maps are usually more detailed than OSM - most 
(all?) areas in OSM don't map detail like where the running lanes of a 
road end and the walkway begins and few areas have individual buildings 
mapped.  For example, zoom into some of the residential streets on: 
http://maps.swansea.gov.uk/localview/OnTheMap.aspx

I'd be pretty interested to hear another side to the argument though. :)

  - Steve
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Re: [Talk-GB] Oneway assumes cars?

[Steve Hill]

On Wed, 24 Sep 2008, David Earl wrote:

> Now there's an interesting thought: instead of changing the map to match the 
> environment, we change the environment to match the map!

Can't remember where the quote comes from (probably the OS), but something 
along the lines of "very occasionally you will find that the map does not 
match reality.  In these cases, reality is wrong." :)

  - Steve
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Re: [Talk-GB] Oneway assumes cars?

[Steve Hill]

On Tue, 23 Sep 2008, Dave Stubbs wrote:

> whether you can just cycle the wrong way down
> the road avoiding any on coming cars.

I _think_ that is illegal in the UK anyway isn't it?  Cycles generally 
have to follow the normal rules of the road unless there is a sign 
explicitly making some exception (I've never seen a "one-way for everyone 
except cycles" sign in the UK).

Of course, technically there should probably be a way of specifying the 
one-wayness of a way for each type of transport.  It can even apply to 
pedestrians - a footway which goes up/down an escallator would be one-way 
for pedestrians.  Then there are things like ski pistes, which are 
slightly harder since there is no rule saying you can't walk up the slope, 
but you probably don't want to. :)

  - Steve
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Re: [Talk-GB] Cameras?

[Steve Hill]

On Mon, 8 Sep 2008, Ed Loach wrote:

> I'd like a cheap digital camera to use when I'm out noting things for 
> mapping purposes; our existing camera eats batteries.

I have an old Canon IXUS 400 that I picked up off ebay, which I find is 
pretty reasonable as a simple and small point & shoot for when I don't 
want to lug around my SLR.  I do tend to find that the battery life of the 
camera is the limiting factor when I'm mapping on foot (camera turned on 
the whole time), but the batteries are quite small so carrying a spare 
wouldn't be a problem.

Pretty robust, optical viewfinder, takes compact flash, rechargable 
lithium ion battery, a bit of optical zoom, 4 megapixels and the lens 
seems good enough to make use of the resolution.  I think the newer IXUS 
models have removed the optical viewfinder though, which is a shame.

> Can anyone suggest either a camera or a good comparison website.

http://www.dpreview.com/ is pretty good for comparing cameras.

> Alternatively if anyone can recommend some good quality, reasonably 
> priced, high capacity rechargeable AA batteries that work well in their 
> digital camera then that may work out a cheaper option.

I used to use 4 AA size NiMh cells in my old HP Photosmart 850, which 
seemed to last well enough and you can now get some fairly high capacity 
(2800mAh or more) cells.  NiMh cells do suffer from a short shelf-life 
though, so it is very much a "charge just before you need them" option, 
whereas lithium ion batteries will hold their charge for ages when not in 
use so your camera can always be ready for use.  But you won't get AA size 
lithium ion cells, so NiMh is about your best option.

  - Steve
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Re: [Talk-GB] Very accurate GPS devices

[Steve Hill]

On Fri, 29 Aug 2008, Tom Hughes wrote:

> He was referring to a combine using a DGPS system which has a base
> station at a fixed point on the farm whose location is well known. It
> then compares that known location to one calculated from the satellites
> in the normal and broadcasts the difference to the mobile received on
> the tractor/combine which uses the difference to correct it's own
> calculated position.

A DGPS station actually works out how big an error each received 
satellite signal has and transmits that data to the (mobile) GPS receiver, 
which then applies the correction _before_ calculating the location. 
(i.e. the DGPS signal contains the timing errors for each satellite rather 
than the errors in the coordinates, since the errors in the calculated 
coordinates would depend on which satellites the GPS is using, which is 
something the DGPS transmitter doesn't know).

I suspect that a system that accurate is probably not just using DGPS 
though - it probably has a set of ground-based transmitters at known 
locations that it uses for ranging as well.

  - Steve
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Re: [Talk-GB] [OSM-talk] Corporate Cartographers accused of demolishing history. (make press release?)

[Steve Hill]

On Fri, 29 Aug 2008, James Stewart wrote:

> I guess one way to break up UK mapping data monoploy is for other
> owners of important GI to release it, such as local authorities,

I was under the impression that the local authorities generally used an OS 
base map, so their own data may well be derived from the OS data.

  - Steve
xmpp:[EMAIL PROTECTED]   sip:[EMAIL PROTECTED]   http://www.nexusuk.org/

  Servatis a periculum, servatis a maleficum - Whisper, Evanescence


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