[OHM] A question regarding coast lines

Thu Sep 5 17:00:00 UTC 2019

Guilherme -

Fantastic! So glad you are finding it useful. Please share the links to
what you're working on - I think plenty of people would love to check it
out!!

So, you're hitting on some tough topics & I'll do my best to answer,

1. Shorelines. Shorelines, as in the boundary between continents and oceans
/ major bodies of water can be tricky for now. OSM actually handles these a
bit differently from other objects / relations. You can see more about that
here: https://wiki.openstreetmap.org/wiki/Coastline It's something we will
be working on in the future, as how coastlines change over time is super
interesting & important, as you point out. But, the good news is...

1.a. You can temporarily (sorry!) work (hack?) around changes in shorelines
until we get that fixed / working (hopefully in the next couple months) by
putting a lake in the middle of your ocean. Any non-coastline body of water
is treated just like anything else with start_date and end_date tags. You
can see an example of this in a mockup of early Seattle I'm working on
here:
http://openhistoricalmap-1936150974.us-east-1.elb.amazonaws.com/#map=17/47.59962/-122.33220&layers=O

2. For two time frames for the same object - e.g. where attributes for that
object are changing over time, that's also an issue at the heart of this
project: how do you track changes to an entity over time - e.g. name,
parent/territory (e.g. of a country / city), paving of roads,
electrification of train lines, etc. There are issues with almost every
proposed solution for data structure, but I think we'd want some sort of
upstream object that ties downstream objects (e.g. our OSM data types)
together, etc., but we aren't there yet. And, as always, we're looking for
solutions. In the mean time, my only suggestion for workaround is to
duplicate the objects in place, put an end date to the non-electrified
lines, and then add a start date and electrical tags for the electrified
lines. I've done that with the roads/streets in Seattle.

2.b. I think that's close to the same thing as 2., but for the time being,
I would suggest that JOSM filters are your best best friend. And, thinking
about how to tag things to make filtering easier is also a must. One thing
I've started doing is tagging things with year tags... like y1855=yes for
info that is shown on an 1855 map. Then, if data is shown on multiple maps,
you can add y1878 (e.g.). Then, you can filter to just see things from that
year.

[image: image.png]

Thanks & keep the questions coming!!

Regards,
Jeff

On Wed, Sep 4, 2019 at 6:17 PM Guilherme Braga Alves <gbragaalves at gmail.com>
wrote:

> Hello guys!
>
> I found OpenHistoricalMap recently, and I'm having a great time with it.
> I'm from Rio de Janeiro, and my first goal is to map the various lines of
> trams we had in the city until the 1960s.
>
> This work has been easy, but I have faced some problems. Since I didn't
> find answers in FAQs or similar things, I forward my doubts.
>
> 1. How do I map changes on the coastline? The history of Rio in the 20th
> century is marked by numerous embankments on the waterfront, so the map
> would be more interesting if it were possible to reproduce these changes.
>
> 1.a. Same for ponds and piped rivers. What should I do to reproduce these
> changes over time?
>
> 2. One of the railroads I am mapping was built in 1878, but was not
> electrified until 1945. Is there any way to insert two time frames into the
> same object?
>
> 2.b. One of the trolley lines I mapped has been converted into a heavy
> railroad track. Should I map two overlapping lines or is it possible to
> time differentiate them using tags?
>
> Thank you for your attention.
>
> --
> *Guilherme Braga Alves*
> Bacharel em *Relações Internacionais* pela *UFRJ - Universidade Federal
> do Rio de Janeiro*.
> Mestre em *Políticas Públicas em Direitos Humanos* pelo *NEPP-DH/UFRJ -
> Núcleo de Estudos de Políticas Públicas em Direitos Humanos da Universidade
> Federal do Rio de Janeiro*.
> Doutorando em *Geografia* pelo *IGEOG/UERJ - Instituto de Geografia da
> Universidade do Estado do Rio de Janeiro*.
> Telefone: (21) 97982-7869.
>
> _______________________________________________
> Historic mailing list
> Historic at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/historic
>

-- 
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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