[HOT] HOT carto, Re: Buildings and residential areas: Buldings as nodes (Q1)

Andrew Buck andrew.r.buck at gmail.com
Thu May 25 21:49:05 UTC 2017


As you say, you looked on the wiki and it does list building nodes as
acceptable.  Mapping them this way is not wrong, it is just far from
optimal.

Regarding the plugins for josm, I don't know that either of these are
really needed.  Residential areas as convex hulls can be easily made in
qgis and then imported into OSM if that is desired, however this was
done by someone a while back (during the Ebola activation in west
africa) and for most areas the result was OK but it still took a lot of
manual work to merge them in anyway, so just drawing them by hand is
almost faster anyway.

For the second one, to convert nodes to areas for buildings you don't
need a plugin as there is already the replace geometry tool in josm
which does exactly this.  If you are doing many hundreds, then the
conflation tools plugin works in conjunction with replace geometry to
match nodes to buildings and then "replace geometry" on each match
automatically.  So a plugin is not really needed.

So to summarize my overall points.  Mapping as a node is not wrong, but
I would rather see someone spend an hour mapping a few hundred buildings
as areas rather than a few thousand as nodes, since the nodes will have
to be mapped as areas eventually anyway.  So as far as I see it it is
just a wasted hour of mapping.  Remember, we are mapping the whole world
and we aim for completeness.  We will achieve this, so why do something
half way, just do it fully the first time so it doesn't have to be done
again.

-AndrewBuck



On 05/25/2017 02:07 PM, Bjoern Hassler wrote:
> Hi all,
> 
> so I don't want to revisit the whole discussion, but here's my view. This
> isn't a suggestion to change the HOT-default of mapping buildings as way,
> but just to explain my approach. I've recently mapped about 2,000
> node-buildings near Fiwila, Northern Zambia. I checked the OSM wiki, it
> said node[building] is ok, and so I went ahead. I also mapped a bunch of
> roads. The reason I did this is because I've previously collaborated with
> one of the health workers there, who is now in Fiwila, and so I wanted to
> support their work in he clinic there (where there's very poor mobile
> signal, people are paid tiny salaries, no mains electricity....).
> 
> So we now know the number of houses (as nodes), and the roads for how to
> get there. From a pragmatic perspective, I think that's ok for our
> purposes. Here are some considerations:
> 
> (1) The node[building=yes] are not rendered in standard carto, HOT carto,
> nor by maps.me. However, OSMAND displays them as building icons. My
> preference would for the buildings to be rendered by maps.me and HOT carto.
> However, I do understand people's concerns.
> 
> (2) Could I have traced these nodes as ways? It took me a while as it
> stands (as the buildings are spread out over some areas), so I don't think
> i would have mapped as many if I had traced them. I also think that for our
> application ("knowing where people are") it's not that relevant.
> 
> So what else could I do?
> 
> (a) Rather than pasting nodes in the centre of the building, I could have
> pasted a small 4m by 4m square, either aligning with centre of the
> building, or even try to paste onto an edge of the building, and just leave
> them like this (half finished). These would render, but would potentially
> be considered "mapping for the renderer", so not ideal. However, they would
> be easier to extend to the proper building outline later (as the tag is on
> the way already, and one node may be in place already). So maybe that would
> have been preferable? Are there any strong views against that?
> 
> (b) Alternatively, I could have just marked residential areas. I switched
> to that a bit later just to try it, and perhaps that is the better
> solution. I.e. "If you cannot map building outlines, just map residential
> areas instead". Residential areas don't render amazingly, but they do
> render. However, it doesn't help knowing how many households there are -
> but perhaps that's ok for us too.
> 
> We're also trying to write some JOSM plugins:
> 
> (1) A plugin that can take a set of buildings, and create the residential
> area automatically, as a concave hull. (We'll post soon about this.)
> 
> (2) Potentially a plugin assists the user in converting node[building] into
> way[building]. As John mentioned, I do think the building plugin is really
> useful, and it seems feasible to add some functionality to it for
> converting from node[building] into way[building].
> 
> Generally speaking, I'm keen on developing tools that can help speed things
> up, making processes more user friendly, more reliable, etc. More on that
> soon.
> 
> Anyway - just my thoughts on the matter!
> Bjoern
> 
> 
> 
> On 25 May 2017 at 17:49, john whelan <jwhelan0112 at gmail.com> wrote:
> 
>>> Buildings as nodes is not a recognized way of mapping them that has
>> broad support.  Almost without exception the only people doing this are
>> newbie HOT mappers who don't know the correct procedure.  So this is a
>> mistake that should be fixed, just like non-square buildings or
>> unconnected roads.
>>
>> I do a lot of validation and clean up on HOT projects and in the areas
>> they map.  I usually check the number of edits a mapper has done and in my
>> experience HOT mappers may map a building three times, they may not square
>> buildings, the buildings might be three times the size they should be, they
>> map them in odd shapes.  I see villages tagged building=residential but its
>> very rare that I see buildings as nodes from HOT mappers. Generally they
>> look at the training guides which describe mapping buildings as ways.
>>
>> The mappers I have seen using nodes for buildings, typically tagging nodes
>> building=hut, are generally experienced mappers who have used nodes for
>> street numbers in the past often from Europe. When I come across them I
>> generally mention that the HOT convention is to map the outline.
>>
>> The concerns I do have about mapping buildings as ways are more on the
>> data quality side. I'm currently looking at Malawi and I'm seeing a number
>> of sites where buildings have been mapped multiple times and I've added
>> tags to a few hundred that have been left area=yes.  Some of these are more
>> than a month or two old.
>>
>> Personally I'd like to see more use of the JOSM building_tool plugin
>> because at the moment there are many areas where you cannot depend on all
>> the buildings having been mapped, mapped just the once or that the area of
>> the building is anywhere near correct.
>>
>> Cheerio John
>>
>> On 25 May 2017 at 11:08, Andrew Buck <andrew.r.buck at gmail.com> wrote:
>>
>>> The real solution is to "upgrade" these nodes into properly mapped
>>> buildings with a way.  We really should be discouraging people mapping
>>> as nodes like this as it is largely a waste of time since someone has to
>>> map it as a way later on anyway and when they do they either need to
>>> delete the existing nodes or merge them into the buildings to preserve
>>> history (but also taking much longer).
>>>
>>> Adding renderings to maps only encourages people to take the easy way
>>> out in the short term and create more bad data.  We should not encourage
>>> this and should be actively trying to fix the nodes already in the
>>> database.  I have done this on a few occasions and have probably knocked
>>> out a few thousand of them, but unless we get serious about cleaning
>>> them up we will end up with more and more of them.
>>>
>>> Buildings as nodes is not a recognized way of mapping them that has
>>> broad support.  Almost without exception the only people doing this are
>>> newbie HOT mappers who don't know the correct procedure.  So this is a
>>> mistake that should be fixed, just like non-square buildings or
>>> unconnected roads.
>>>
>>> -AndrewBuck
>>>
>>>
>>> On 05/25/2017 04:09 AM, Bjoern Hassler wrote:
>>>> Hi all,
>>>>
>>>> just to follow up on the buildings discussion - it seems that it's not
>>>> likely that node-buildings will be rendered in the standard cartography,
>>>> see https://github.com/gravitystorm/openstreetmap-carto/issues/806.
>>>>
>>>> However, I think there is a case for rendering node-buildings in the HOT
>>>> cartography? I'll file a suggestion here: https://github.com/
>>>> hotosm/HDM-CartoCSS.
>>>>
>>>> Bjoern
>>>>
>>>> On 23 May 2017 at 04:54, Rob Savoye <rob at senecass.com> wrote:
>>>>
>>>>> On 05/22/2017 01:44 PM, john whelan wrote:
>>>>>
>>>>>> consider and it is a major part of engineering.  No matter what
>>>>> compression
>>>>>> system is used four nodes will always take up four times the space as
>>> one
>>>>>> node.  Maybe not with .7z compression looking for strings in the long
>>> lat
>>>>>> but its a good rule of thumb.  Again OSM is now running the largest
>>>>>> database known in whatever it is running in, I forget the name.  It's
>>>>>
>>>>>   OSM uses PostgreSQL with the postgis and hstore extensions. I run it
>>>>> locally to save on bandwidth latency, plus it works offline too cause
>>>>> connectivity is poor around here. Mobile bandwidth is getting better
>>> all
>>>>> the time all over the planet though. Adding data to OSM is better to be
>>>>> done the way most others do it than worrying about bandwidth.
>>>>>
>>>>>   Looking into a few OSM files, I see <node> used as a building that
>>>>> hasn't been mapped as a polygon, ie.. just a waypoint. That's useful
>>>>> enough for most people trying to find someplace. For a building that
>>>>> actually has it's dimensions mapped, then it's a <way>, with references
>>>>> to each <node>. It depends what type of info you want from your map.
>>>>> When generating a display map, a <node> won't appear as a building,
>>>>> it'll just be a cute icon. If you want to see a whole building shape,
>>> it
>>>>> needs to be a <way>. Some buildings have both.
>>>>>
>>>>>         - rob -
>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>
>>>>
>>>>
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