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

Mon May 22 18:16:43 UTC 2017

Hello all,

There's really no "their" where OSM is concerned - the database is made by
individual contributors, without centralized oversight, and much of the
mapping is by convention. But looking at the OSM wiki gives some fairly
strong recommendations: http://wiki.openstreetmap.org/wiki/Key:building -
to paraphrase, "in absence of better data, building-as-a-node is better
than nothing at all, until it can be mapped as an area from a better
source."

As far as "accurate mapping" - that's a problem and a driving force for the
whole of OSM: have you seen the map in 2010? There was a very similar
situation worldwide, with most buildings existing as rough outlines or not
at all; requiring "perfect or nothing" would have resulted in no OSM,
period.

That said, the quality of mapping does depend on feedback, especially with
new mappers: is the project with badly mapped buildings representative of
HOT projects? The ones I've seen (and edited) seem to match building shapes
and sizes well - e.g. http://tasks.hotosm.org/project/2520 - but that's
also an issue of task validation, in addition to mapper training; I do
agree that takes some additional human power in return for much better map
result.

So, I guess that where time is critical (or space, even though XML
compresses well and data for mobile apps is compressed even more
efficiently), buildings-as-nodes are an acceptable interim solution, but
the ideal case is buildings as well-outlined ways (which is what
"experienced OSM mappers" do prefer, btw; no retraining needed).

Cheers,
Jan "Piskvor" Martinec,
OSM and HOTOSM mapper

Dne 22. 5. 2017 17:54 napsal uživatel "john whelan" <jwhelan0112 at gmail.com>:

> But from your computer science background you should realise there are
> costs involved.  To mark a building as a node is one line in the database.
> As a way well there are four nodes for a start each with its lat and long,
> then you have the connecting way.  Have you saved a bit of .OSM and opened
> it in Notepad++?  Try it sometime.  Open JOSM download a tiny area ie a
> building and take a look.  Download a node and take another look.
>
> So we have time costs in mapping, plus internet costs in uploading the
> additional information, storage in the main OpenStreetMap database,
> additional costs in downloading, more storage required on smartphones in
> the field more processing required at all stages. The time costs in mapping
> mean given the number of mappers we have few projects will get mapped. We
> also have experienced OpenStreetMap mappers mapping who may not follow HOT
> guidelines.  These will need retraining and how will you reach them?
>
> In Africa internet transmission costs are much higher than locally in
> North America so ideally we want to minimise these.
>
> Then you get to the added value.
>
> Take a look at http://tasks.hotosm.org/project/2656#task/102 when I
> validated it recently for a highways project it seemed to me that most
> buildings=yes were twice or three times the size of the building sometimes
> covering more than one building, at least they were mostly square.  For HOT
> projects this is not untypical but strange shapes tagged building=yes
> abound. I've seen tiles when only half the buildings have been mapped but
> the tile marked done.
>
> The true added value is being able to estimate population. How many people
> are there that need to be vaccinated.  If the buildings are mapped
> accurately then you stand a chance.  You may have seen some references to
> the JOSM building_tool plugin, try it if you haven't.  You take the number
> of buildings and their combined area and you can make some reasonable
> guesses. The area data is so unreliable you might as well have asked for
> nodes and to be honest you stand a better chance of them all being mapped.
>
> I take it you took all these points into consideration before saying that
> building=yes nodes should not be used?
>
> The place to raise the issue is with OpenStreetMap, its their map and
> there will be different points of view and it might be worth checking how
> many there are in the map already.
>
> Cheerio John
>
> On 22 May 2017 at 11:18, Enock Seth Nyamador <kwadzo459 at gmail.com> wrote:
>
>> On personal level I feel mapping buildings as nodes is very wrong so I
>> avoid it.
>>
>> But I think tagging nodes as building should be looked at very well. I
>> will recommend it is deprecated.
>>
>> Best,
>>
>> - Enock
>>
>> 2017-05-20 11:38 GMT+00:00 Vao Matua <vaomatua at gmail.com>:
>>
>>> My opinion is that buildings should be mapped as areas.
>>> In un-mapped areas it would be best to create landuse=residential areas
>>> first rather than quickly tagging buildings with single nodes. When it
>>> comes time to trace buildings it is troublesome to convert single nodes to
>>> polygons.
>>> For existing single node areas they could be cleaned up on an as-needed
>>> basis.
>>>
>>> Emmor
>>> (Palolo)
>>>
>>> On Sat, May 20, 2017 at 2:10 PM, Bjoern Hassler <bjohas+mw at gmail.com>
>>> wrote:
>>>
>>>> Dear both, dear all,
>>>>
>>>> If we're agreed that it's better to map buildings as areas - should we
>>>> try to re-map node-buildings from previous campaigns as areas? Or shall we
>>>> just leave it?
>>>>
>>>> Many thanks,
>>>> Bjoern
>>>>
>>>> On 19 May 2017 at 17:54, Cascafico Giovanni <cascafico at gmail.com>
>>>> wrote:
>>>>
>>>>> AFAIK Osmand renders addr: housenumber also for polygons [1].
>>>>>
>>>>> Anyway I agree to the general rule that rendering has to adhere to
>>>>> mapping (and not VS).
>>>>>
>>>>> [1] cascafico.altervista.org/public/Screenshot_2017-05-19-18-40-41.png
>>>>>
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