On 08/19/2015 05:29 AM, Nathan Mixter wrote:
In any discussions about land use and land cover, we should look at
what organizations have done and how they have mapped ares. For
instance, in USGS imagery in JOSM you can see how they render borders
with just a dashed line and let the land cover have various shades of
color on top of it.
The U.S. Forest Service has a distinct classification for mapping
vegetation within the forest. And the USDA differentiates between use
of forest land and forest cover
(http://www.ers.usda.gov/data-products/major-land-uses/glossary.aspx).
Here is how the USGS defines land use and land cover
(http://www.mrlc.gov/nlcd92_leg.php and in more depth at
http://landcover.usgs.gov/pdf/anderson.pdf). Not sure how other
countries map land use and land cover, but this is a sample from what
the U.S. does.
>From
http://www.ers.usda.gov/about-ers/strengthening-statistics-through-the-interagency-council-on-agricultural-rural-statistics/land-use-and-land-cover-estimates-for-the-united-states.aspx#h
"Land use and land cover are often related, but they have different
meanings. Land use involves an element of human activity and reflects
human decisions about how land will be used. Land cover refers to the
vegetative characteristics or manmade constructions on the land’s
surface."
I hear a lot of argument here, and much of it is philosophizing. Let me
offer another argument. Deficiencies in the standard rendering are
leading us to impose constraints that do not exist. The very idea that
we should have to cut out watercourses and highways from a National
Forest to show it correctly on a map is absurd. If the renderer cannot
cope with the idea that the Elm Ridge Wild Forest (a protected area -
and specifically an area of state ownership with public access for
recreation and harvesting of fish and game) lies partly within and
partly outside the Catskill Park (a different sort of protected area,
not all under state ownership) and in turn has several bicycle corridors
(an area of less protection) overlaid upon it, then it cannot cope with
the messy reality that I work with locally.
Since I render my own maps, let me begin by observing: THE LACK OF
CONSENSUS ON THESE ISSUES MEANS THAT I DO NOT USE OSM AS A DATA SOURCE
FOR PROTECTED AREA BOUNDARIES. I go to alternative, mostly government,
data sources for the boundaries of government and other protected lands
and use them for map production. I simply cannot cope with wholesale
retagging of these areas every few months as each new tagging scheme
comes through. WE NEED TO REACH SOME SORT OF STABLE CONSENSUS, at least
one that lets us produce medium-scale maps suitable for general use
without running on a hamster wheel of patching renderers to adapt to
changing tag schemes.
I've half come around to the position that National Forest boundaries
don't belong in our database at all. They're often not any more
observable on the ground than any other property lines - and I believe
that we reached a consensus that delineating land ownership is outside
the scope of OSM. (Am I wrong about this?) In fact, the reason that I'm
able to ignore OSM on the point is that most of the data I need is
available in authoritative form from the agencies that manage the land.
Unfortunately, some of the smaller agencies (mostly county and municipal
agencies) still haven't moved forward into using GIS, or simply don't
have the resources to make what GIS data they have available to the
public, so there's still some amount of measuring on paper maps. I'd
done a few local nature preserves that way (along with cross checking by
hiking to corners and collecting GPS waypoints), and it had been
convenient to use OSM as a store for the data so collected, but I'm
willing to give that up and go back to holding the data privately and
rendering them as another layer - doing an export from OSM to my own
data store. Again, the features are hard to observe in the field. It's
quite an interesting hunting expedition, trying to find the corners of a
county nature preserve where the adjoining landowner doesn't trouble to
post the land. Sometimes it involves trying to locate survey pins with a
metal detector in dense forest.
Since we don't have a good general policy for OSM maintenance of data
where the authoritative copy is elsewhere, OSM really simply becomes the
convenience of "one stop shopping." I enjoy having that convenience, and
so do many other users. But for some of the data, it simply costs too
much time and effort to negotiate the minefield of tag wars.
And I still claim it's largely because of the renderer.
So now let me move forward to specific rendering suggestions - noting
that that I'm here as a field mapper (I mostly do hiking trails and
associated facilities, and for the most part don't armchair-map
anything), a consumer of OSM data (I produce my own maps for my
GPS-equipped smartphone, because I find them more useful than anything I
can buy), and a Mapnik user (I have my own Mapnik scripts. What the
Standard renderer does is of little consequence to me.) I still think my
approach to the general problem of rendering the competing ideas of land
use, land cover, and land administration may be useful.
Refer, if you will, to
http://kbk.is-a-geek.net/catskills/karl.html?la=42.3024&lo=-74.1807&z=13
This is a fairly conventional "topo map" rendering in a style intended
to be of use to hikers navigating using a GPS unit.
There are numerous administrative units, some overlapping, shown here.
The most significant is the Catskill Park. This unit is truly one of a
kind - it is enshrined in New York State's constitution, and takes a
constitutional amendment to change it. It does not reflect land
ownership or land use but merely land administration: the Department of
Environmental Conservation serves as a "super zoning board." You can
see, for instance, to the west, that the village of Windham with its
extensive ski resort is located entirely within the boundaries of the
Catskill Park. Rendering this boundary in blue defies all topographic
map convention, but is a longstanding tradition in New York. Anyone
living in the Park knows the significance of the Blue Line.
To the east, you'll see at least two different protected areas, the Elm
Ridge Wild Forest and the Windham-Blackhead Range Wilderness. Wild
Forest is a lower level of protection than Wilderness, and allows such
uses as mountain biking. Showing these parcels separately is essential
to a mountain bike user, since it will indicate how far s/he can legally
ride on the trails. Note that the Elm Ridge Wild Forest extends outside
the Blue Line at the north. The area outside enjoys protection as a Wild
Forest, but does not enjoy the protection of the Catskill Park. The
state is free to classify the land as other than Wild Forest, sell it,
or develop it by a simple act of the legislature, a much lower hurdle
than amending the constitution.
You'll see how the parcels can be shown readily by using a
semitransparent shading on the interior edge of the polygon, without
obscuring what lies within.
Shown in the base color is land cover with deciduous forest (medium
green) predominant. At the highest elevations and in the wet low-lying
areas, coniferous forest (dark green) takes over. There are some patches
of mixed forest (lightest green) along with farmland (buff), marshland
(aqua) and developed land (pink) in the valleys. Some of the cliffs have
patches of bare rock and scree (grey). A light hill shading overlays the
whole.
So here we have large administrative units (lines with their names shown
on the interior), smaller and sometimes overlapping administrative units
and land use designations (lighter lines with transparent color overlay
on the interior, with names in the interior for the larger areas where
possible), hill shading, and land cover (base color) all shown. The
visual clutter can get pretty bad in spots, particularly where different
agencies' GIS systems fail to agree, but the information density is high.
Patterned overlays are also still available, and I'm not using them very
much yet. You can see that I mark emergent wetlands (from yet another
data source) with a pattern, if you use the mouse wheel or zoom buttons
in the map that I linked to to examine the wet area north of Hensonville
at the center. Showing these without a rendered boundary seemed
appropriate, since they're approximate at best (and depend on rainfall
and beaver activity in any given year).
I contend that if the standard rendering made more use of edge in-fill,
pattern fill, and transparent overlays, we'd have fewer arguments. With
our use of solid color fills (and opaque pattern fills) exclusively, we
simply don't have enough ways of displaying the competing concerns, and
lurch among tagging that focuses on land ownership, land administration,
land use, and land cover - all related, but distinct concerns - with
cascading effects downstream as people try to render whatever tag scheme
has come out of the latest round of a never-ending argument. In large
measure, it comes down to the renderer. We try to have a tag scheme that
says, "this parcel is inside the Catskill Park. It's owned by the
Department of Environmental Conservation. It's open to the public. It's
covered with balsam forest. It's managed as Wilderness Area" in a single
statement. That simply will never be successful. Renderers will have to
deal with these cross-cutting concerns, which means rendering
overlapping areas that have different meanings.
We might as well face the fact that these issues are chaotic, they're
always going to be chaotic, and no tag scheme will ever describe them
fully. But please, can we try at least not to have continual breakage
for major, signed features such as National Forests or the Catskill Park
that nearly all map users will want to have rendered somehow?
--
73 de ke9tv/2, Kevin
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