[OHM] Some mapping questions

[Jeff Meyer]

Hannes - Welcome aboard & THANK YOU for your reat questions & initiative.
Please be patient or provide your opinions, as we haven't figured
everything out yet.  I'll do my best below. Anyone else, please join in!

p.s. love your old mapping!!

On Fri, Jul 10, 2020 at 2:22 PM Hannes Röst <hannesroest at gmx.ch> wrote:

> Dear list
>
> Hi, I have just started to map with OHM and it has been a fun ride. I do
> have a few questions:
>
> 1. Mapping pre-historic buildings, I am not sure how to encode times
> before 1582 since they require additional conventions according to ISO 8601
> [1] and it would be great to clarify this, I have now used the conversion
> of 3384 AD = -3383, see my buildings here [2]. Can you comment on whether
> this is the right way to do it? It is counter intuitive to be "one year
> off" but I think its most consistent to use ISO 8601, however this should
> be clarified on the wiki.
>

I myself just noticed that 1582 issue the other day. I think a "loose"
answer is that we loosely use the 8601 format (i.e.., YYYY-MM-DD) for
entering our tags, but not for processing those tags, if that makes sense.
So, your example is likely fine, but I am curious - did you mean "AD" or
"BC"? And, so we have year-level precision that far back?


> 2. I noticed on the mailing list some discussion about OSM imports and I
> cannot help but notice that major geographical and political features are
> missing in the areas I am interested in (eg lake Constance and Lake
> Ontario) and to me it seems like a reasonable idea to get things off the
> ground and tag imports with "licence=ODbL" for things like country
> boundaries and mountains/rivers/lakes. I am not sure whether spending a lot
> of time re-mapping geographical features simply so that they are under CC0
> is a good use of (my) time. I am happy to have all content by default under
> CC0 but it seems like we would duplicate a lot of work simply for the
> purpose of having it under CC0.
>

I am guilty of this crime. I'm not sure why, but when we did an initial
planet import from OSM, a loooooong time ago (~2012), I fear we (I) missed
some pretty important natural features. In particular, inland lakes. These
need to be restored and I would suggest the best way to get them fixed is
a) import from a CC-BY-SA source like fosm.org. I agree that that's not a
good use of your time. How about if you let me know which areas you'd like
/ that would be helpful, & I'll prioritize adding those myself. We have a
ticket for this open here:
https://github.com/OpenHistoricalMap/issues/issues/4. In addition, there is
much more CC0 data available than there was at the time of the initial
creation of OSM's data.


> 3. Furthermore, I see rivers etc mapped in changeset 1 [3] and I wonder
> whether that data is truly CC0 or also from some OSM import / satellite
> (probably depends on how the import was done). I have used ESRI images to
> trace lake Constance since ESRI is free of restrictions and will produce
> CC0 content but I dont know about other imaging data and whether it has
> been used in OHM
>

Changeset 1 was the initial planet import & you are correct. That likely
took place shortly after the OdBL switchover in OSM. This data should not
be redistributed in any form util we resolve this issue.

Bing and a few others have authorized OHM use of their imagery. Richard
Welty can comment on that & he may have already annotated it in the wiki,
but I'm not sure.


> 4. I would like to ask how replaced structures should be handled such as
> the bridge [4] which was built in 1520 replaced 1828 with another wooden
> bridge and finally replaced in  1839 with the (current) stone structure. I
> saw some mention on the mailing list with reference to the date namespace
> [5] and I wonder whether this has consensus and how to handle a complete
> replacement -> would it be better to have 3 separate ways here that have
> independent start/end dates since these are completely different bridges.
> It seems the date namespace makes more sense if roads change names or
> importance but is not intended for a different physical object. Personally
> I would prefer the different ways solution since one could then refer to
> these entities using a unique identifier for each (eg in Wikidata).
>

We're currently trying to figure this out. We do not recommend adding the
years into the name tag. Right now, I think the 2 approaches are:'
1) Do 3 different ways. This is currently a pain for editing, but will
eventually be a bit more correct, esp. if the bridges had separate physical
spatial geometries.
2) Do 1 way associated with 3 relations. This will help ease editing, as
there are fewer individual ways, but could allow for different Wikidata
tags, names, materials, and other properties. It also gives a more stable
OHM identifier for the bridge. The type of relation is still not clear, but
we're actively trying to figure that out / open to suggestion.


> 5. How should data from a map best be tagged? I have used the "as_of" tag
> since I dont know the exact starting time for a road on a map, I only know
> it was present at a certain time. However, this leads to some rendering
> artefacts: the roads will be there from the beginning of time, however the
> bridge for which I know when it was built will suddenly appear in 1520 and
> before 1520 there is simply a hole where the bridge was [4]. Any
> suggestions on how to deal with this situation? Would it be better to use
> "after 1838" for a map produced in 1838, how would that be rendered? (see
> suggestion here [6])
>

Right now, the renderer doesn't pay attention to "as_of" - that's more for
data enrichment. I would suggest making an arbitrary assignment as to your
best guess, and annotate that it needs to be fixed, either with something
like: fixme=start_date or start_date:note=estimate.
We're still trying to figure out best conventions & would love your input!


> 6. Similarly, I have traced the data of a river from a map of 1838 and the
> course of the river has changed quite a bit. Now using the "as_of" tag now
> means that there are 2 rivers displayed in the map which is not really what
> I wanted. [7] Any thoughts on best to handle this? Of course I could choose
> an arbitrary start/end date to switch from one river to the other but
> without more information this is not optimal either.
>

You should add a "start_date=" to the current river path that matches the
"end_date=" of the old river course. This might also be handled by
relations, where the relation stays constant, but the river geometry
changes on the member relations underneath.

I think I've done something similar (without the relations) at:
Krakow (actually different... just added a split to the river:
https://www.openhistoricalmap.org/#map=14/50.0601/19.9400&layers=O
Seattle (partway through changing the course of the Duwamish... need to fix
this): https://www.openhistoricalmap.org/#map=14/47.5413/-122.3250&layers=O


> 7. I have another bridge where there is clear evidence
> (dendrochronological) when it was built, around 150 BC, but unclear when it
> was destroyed. We only know that its defunct today, so it was destroyed
> somewhere between 150 BC and 2020 BC, how should that best be tagged?
>

Hmm... tough one. I think we need a tag like fixme=end_date, but maybe
something that implies more of a hunt / research project than that little
tag would hint at.


> Best regards
>
> Hannes
>
> 1. https://en.wikipedia.org/wiki/ISO_8601#Years
> 2. https://www.openhistoricalmap.org/relation/2690490
> 3. https://www.openhistoricalmap.org/way/4515328
> 4. https://www.openhistoricalmap.org/way/198531945
> 5. https://wiki.openstreetmap.org/wiki/Proposed_features/Date_namespace
> 6. https://wiki.openstreetmap.org/wiki/Key:start_date#Approximations
> 7. https://www.openhistoricalmap.org/#map=16/47.5895/8.9490&layers=O
> 8.
> https://www.openhistoricalmap.org/way/198531929#map=18/47.55831/9.09103&layers=O
>
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>


Regards,
Jeff

-- 
Jeff Meyer
206-676-2347
osm: Open Historical Map (OHM)
<http://wiki.openstreetmap.org/wiki/Open_Historical_Map> / my OSM user page
<http://www.openstreetmap.org/user/jeffmeyer>
t: @OpenHistMap
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