[OHM] representing relationships between historic and modern road nets

[Richard Welty]

i just wrote this up to reflect some discussion Jeff and i had on the
last OHM call. i do not have any proposed solutions to the issues i
bring up; i just want to start some discussion.
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i have experimented a bit with the entry of historic highway alignments
into OHM. it has exposed some things we should think through. i've
discontinued work on data entry as i consider what i've done so far to
be a bit unsatisfactory.
The core of the issue is that with historic alignments, in many cases
the physical roads exist today, and if we simply use OSM tagging
standards we duplicate a lot of data. but then, there are realignments
which result in changes in the road, and these need descriptions in OHM.
duplication of data allows for very simple display and data consumption.
if we were to instead have links back to OSM for those things that are
unchanged, there are two issues 1) what is the model for display and
other data consumption and 2) how do we handle situations where physical
change happens in OSM that requires us to update OHM with older data
that's diverged. This i think happens more than we think about; here in
upstate NY new fangled traffic circles are springing up all over.
Here are a pair of links, one to OSM, and one to OHM, that i think
illustrate some of the issues. OSM shows a landscape which has been
dramatically altered by the construction of I 787. OHM shows my partial
reconstruction of the pre 787 map.

https://www.openhistoricalmap.org/#map=15/42.6994/-73.7126&layers=H

https://www.openstreetmap.org/#map=15/42.7011/-73.7135


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