<div dir="ltr">+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.</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Feb 6, 2021 at 10:46 AM Greg Troxel <<a href="mailto:gdt@lexort.com">gdt@lexort.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
Marc Sevigny <<a href="mailto:marc.sevigny@gmail.com" target="_blank">marc.sevigny@gmail.com</a>> writes:<br>
<br>
> Last winter, I worked on mapping stone walls in NH using LIDAR imagery.<br>
> There has been a push in my town (Harvard) to map all stone walls, as a<br>
> cultural and historical resource worthy of protection.<br>
<br>
Certainly a mapper putting real things in the DB is 100% fine, of<br>
course. If the town wants to map them that probably raises issues *on<br>
their end* about control over changing the dataset. If you are just<br>
mapping them as a private activity, not your problem, but I find that<br>
town government's goals and OSM's goals sometimes do not align.<br>
<br>
I would be very interested to know if this has been thought through and<br>
there's a written plan (which would be a public record, I'd think).<br>
<br>
<br>
What was the horizontal and vertical resolution of the LIDAR you used?<br>
In MA near us, I think it's 1m H and also 1m V. It seems to me that<br>
better vertical would really help.<br>
<br>
> I plan on using the same method used in the NH project<br>
> <a href="https://granit.unh.edu/resourcelibrary/specialtopics/stonewalls/" rel="noreferrer" target="_blank">https://granit.unh.edu/resourcelibrary/specialtopics/stonewalls/</a> to record<br>
> them.<br>
<br>
I went to that page and didn't immediately understand the method. I<br>
also don't understand licensing of the resulting dataset.<br>
<br>
Is this just humans looking at LIDAR Shaded Relief (LSR hence) and<br>
drawing, like we'd do in josm? Or is there something more? I am aware<br>
of some other work:<br>
<br>
<a href="https://stonewall.uconn.edu/investigation/mapping-and-gis/#" rel="noreferrer" target="_blank">https://stonewall.uconn.edu/investigation/mapping-and-gis/#</a><br>
<br>
that I think involves processing sort of like hill shading but intended<br>
to find walls and building foundations.<br>
<br>
Do you mean you intend to spend some time looking over LSR in Harvard<br>
and draw walls?<br>
<br>
> I'd tag those that are added as "unverified" until ground-truthed.<br>
<br>
I've been mapping walls, and also field checking, in Stow Conservation<br>
Trust property. Sometimes the signature of stone walls is really strong<br>
and there is little risk of error, and sometimes it's iffy. What I've<br>
done is add "fixme=field check" when I am doubtful. That's a little<br>
loud.<br>
<br>
I think it's excessive to mark everyone unverified; we don't do that<br>
with buildings from imagery.<br>
<br>
So I'd suggest marking unverified=yes (Is there a page/consensus on<br>
this?) only when you are doubtful.<br>
<br>
I would suggest fixme=field check if you are really doubtful and intend<br>
to go check in the next 6 months.<br>
<br>
I have found it useful to map everything I can see and even things that<br>
are iffy with fixme, and then go hike a property and check the iffy<br>
ones. Sometimes they are phantom, and sometimes they are real with more<br>
real wall extending that I didn't perceive.<br>
<br>
I have found the MassGIS LIDAR horizontal accuracy to be excellent, when<br>
compared to dual-frequency 4-constellation RTK.<br>
<br>
> Does anyone have any concerns with this? I would follow the recommendation<br>
> found here: <a href="https://wiki.openstreetmap.org/wiki/Tag:wall%3Ddry_stone" rel="noreferrer" target="_blank">https://wiki.openstreetmap.org/wiki/Tag:wall%3Ddry_stone</a><br>
><br>
> Are there downsides? Could this clutter up rendering?<br>
<br>
I have been adding some based on just me looking at the MassGIS LIDAR<br>
Shaded Relief. I don't feel like there is any problem. I find the wall<br>
line very thin on the standard render, and I perceive it as really<br>
useful, not clutter.<br>
<br>
I don't think you should worry about the effect on rendering at all. If<br>
there is valid data, and the render isn't pleasing to someone, the<br>
people that to the rendering can change that. In my view the problem<br>
with the standard render is the other way around, how it tends to<br>
control tagging.<br>
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</blockquote></div>