[Talk-us-massachusetts] Mapping stone walls

[Brian M. Sperlongano]

+1 to the notion generally of mapping stone walls.  They're useful in
detailed maps of hiking areas and I wouldn't consider them clutter at all.
I map these frequently, and they're often visible in the 2019 spring
overhead imagery in RI.  Normally my method is to snap a photo of a stone
wall each time I walk by one on a trail, and then use the image's geo-tag
in JOSM to match them up with overhead.

On Sat, Feb 6, 2021 at 10:46 AM Greg Troxel <gdt at lexort.com> wrote:

>
> Marc Sevigny <marc.sevigny at gmail.com> writes:
>
> > Last winter, I worked on mapping stone walls in NH using LIDAR imagery.
> > There has been a push in my town (Harvard) to map all stone walls, as a
> > cultural and historical resource worthy of protection.
>
> Certainly a mapper putting real things in the DB is 100% fine, of
> course.  If the town wants to map them that probably raises issues *on
> their end* about control over changing the dataset.  If you are just
> mapping them as a private activity, not your problem, but I find that
> town government's goals and OSM's goals sometimes do not align.
>
> I would be very interested to know if this has been thought through and
> there's a written plan (which would be a public record, I'd think).
>
>
> What was the horizontal and vertical resolution of the LIDAR you used?
> In MA near us, I think it's 1m H and also 1m V.  It seems to me that
> better vertical would really help.
>
> > I plan on using the same method used in the NH project
> > https://granit.unh.edu/resourcelibrary/specialtopics/stonewalls/ to
> record
> > them.
>
> I went to that page and didn't immediately understand the method.  I
> also don't understand licensing of the resulting dataset.
>
> Is this just humans looking at LIDAR Shaded Relief (LSR hence) and
> drawing, like we'd do in josm?  Or is there something more?  I am aware
> of some other work:
>
>   https://stonewall.uconn.edu/investigation/mapping-and-gis/#
>
> that I think involves processing sort of like hill shading but intended
> to find walls and building foundations.
>
> Do you mean you intend to spend some time looking over LSR in Harvard
> and draw walls?
>
> >  I'd tag those that are added as "unverified" until ground-truthed.
>
> I've been mapping walls, and also field checking, in Stow Conservation
> Trust property.  Sometimes the signature of stone walls is really strong
> and there is little risk of error, and sometimes it's iffy.  What I've
> done is add "fixme=field check" when I am doubtful.  That's a little
> loud.
>
> I think it's excessive to mark everyone unverified; we don't do that
> with buildings from imagery.
>
> So I'd suggest marking unverified=yes (Is there a page/consensus on
> this?) only when you are doubtful.
>
> I would suggest fixme=field check if you are really doubtful and intend
> to go check in the next 6 months.
>
> I have found it useful to map everything I can see and even things that
> are iffy with fixme, and then go hike a property and check the iffy
> ones.  Sometimes they are phantom, and sometimes they are real with more
> real wall extending that I didn't perceive.
>
> I have found the MassGIS LIDAR horizontal accuracy to be excellent, when
> compared to dual-frequency 4-constellation RTK.
>
> > Does anyone have any concerns with this?  I would follow the
> recommendation
> > found here: https://wiki.openstreetmap.org/wiki/Tag:wall%3Ddry_stone
> >
> > Are there downsides?  Could this clutter up rendering?
>
> I have been adding some based on just me looking at the MassGIS LIDAR
> Shaded Relief.  I don't feel like there is any problem.  I find the wall
> line very thin on the standard render, and I perceive it as really
> useful, not clutter.
>
> I don't think you should worry about the effect on rendering at all.  If
> there is valid data, and the render isn't pleasing to someone, the
> people that to the rendering can change that.   In my view the problem
> with the standard render is the other way around, how it tends to
> control tagging.
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