[Imports-us] NJ Landuse import (NJ2002LULC)

Reiser, John J. Reiser at rowan.edu
Wed Aug 21 14:32:24 UTC 2013

Hello fellow mappers,

I'm the original importer of the NJ 2002 Land Use data. First, I would
like to say that I am against removing the data outright without a plan to
replace it. While the data was 7 years old at the time of import, it was
the most current, comprehensive land use data available for New Jersey. My
main reservation is that almost all of the original changesets have since
been touched and many of the source tags have been removed.

Background on my import: http://njgeo.org/2010/02/03/updating-osm-lu-data/
Metadata for one of the NJ LULC 2002 datasets:
Salient points from the metadata:
* The data set will provide information for regulators, planners, and
others interested in LU/LC changes, and allow them to quantify those
changes over time using GIS. The use of the updated 2002 LU/LC and IS
layer in change analyses
studies will provide a means of monitoring "the health of the citizens
and ecosystems of New Jersey" through the use of diverse applications.
* Digital color infrared (CIR) orthophotography of New Jersey in State
Plane NAD83 Coordinates, U.S. Survey Feet. The digital orthophotography
was produced at a scale of 1:2400 (1"=200') with a 1 foot pixel
resolution.  Land use/land cover for 2002 was digitized directly from
2002 digital image files.

I would argue that any "simply wrong" areas are ones that have
significantly changed since March 2002. New Jersey provides the source CIR
2002 photography as a WMS, so you can bring it into JOSM to see how the
line work compares. Granted, I did simplify the polygons before converting
them to .OSM, but that shouldn't be the source of completely erroneous
areas. Serge, please direct me to the cemetery-as-school so that I can see
if that was corrected in the 2007 Land Use.

As Greg pointed out, the landuse=scrub is my fault. It should have been
natural=scrub. I must have gotten the landuse/natural tags mixed for that
land use. I've attached the table I used to translate the Level IV
Anderson codes to OSM tags.

I also recognize that the relations are way, way too large. When I
initially simplified and merged polygons, I was left with a "natural=wood"
polygon stretching from Raritan Bay to Delaware Bay with several thousand
interior rings. I used the major roadways of the state to break the
polygons into more manageable chunks, but this still produced polygons
that have 4,000-8,000 vertices (and thus at least 4 outer ways) to enclose
the area. I've been exploring ways to programatically reduce the size of
some of these wooded areas by splitting them further using tracks through
the wood or some other geometry.

Regarding updates, the 2007 Land Use is available:
http://nj.gov/dep/gis/lulc07shp.html and the 2012 Aerial Photography is
also available: 
The 2012 Land Use is not yet available but it is in process and the
estimated delivery date that I've received from our state GIO is mid-2014.
I would be more than happy to work with other interested mappers on the
2007 land use data and develop a plan to replace the existing 2002 data
with the 2012 once it is available.


John Reiser
Geospatial Research Lab <http://gis.rowan.edu/>
Rowan University <http://rowan.edu/geography>
201 Mullica Hill Road
Glassboro, NJ 08028
phone: 856-256-4817
cell: 856-347-0047
twitter: @rowangeolab <http://twitter.com/rowangeolab>

On 8/21/13 6:29 AM, "Serge Wroclawski" <emacsen at gmail.com> wrote:

>On Wed, Aug 21, 2013 at 12:19 AM, Darrell Fuhriman <darrell at garnix.org>
>> I won't argue with your first two points, however...
>>> 3. The import is wrong in a number of places
>>> I don't know if it's because the import is old, but the data is simply
>>> wrong in many areas.
>> Based on what? It's great to declare "it's simply wrong" but there
>>should be a little bit more justification than that. Many areas? How
>>many? How much of the total area do these "simply wrong" areas entail?
>>Why are they "simply wrong"? And further, why is it being "wrong in a
>>number of places" justification for removing everything in its entirety?
>I'll start with your last question first.
>The justification for removing the NJ2002LULC data is quite
>comprehensive, with several points which all support the argument of
>doing so.
>Now, "Based on what"- based on what's actually present on the ground,
>vs what the data says is present. Many areas- not a huge number, but
>I've seen more than a few. How many- I don't know, since I don't
>survey the entire state of New Jersey by hand, but just yesterday I
>found an area that it said was a graveyard that was actually a school.
>Now, unless New Jersey elementary school students have a haunted
>playground, that information is wrong.
>Similarly, I've found areas classified as industrial that were
>residential, etc.
>The data is simply wrong, either out of date, or has always been wrong.
>Nonetheless, this is not the only argument for its removal, and there
>were a total of five arguments I made.
>>> 4. I disagree with many areas' subjective data
>>> One of my bigger frustrations with this import is that I simply
>>> disagree with some of the classifications, especially "scrub", and
>>> this is very typical of landuse classifications- they're highly
>>> subjective.
>> Totally disagree. "Subjective" is not the same as "something I disagree
>I think that's the very definition of "Subjective"- two people looking
>at something and having answers which differ based on the same data.
>> Scrub/Shrub is fairly well defined classification (albeit, one of the
>>less clear ones), with a body of scholarly literature behind it.
>That may be the case, but the data in OSM must follow OSM
>classifications, which differ.
>Areas with trees that are 20+ feet high trees are not "scrub" by my
>working definition of scrub, and they don't match the OSM wiki's
>picture of what scrub means:
>In this case we have a few possibilities:
>1. The classifications NJ uses differ from the classifications OSM uses
>2. There's a problem with the import (rather than the original
>dataset) in what was classified as what
>3. The data was wrong in the NJ2002LULC dataset
>4. My working definition of scrub is wrong, and the wiki should be
>updated for poor souls like me.
>> They have been defined, and photo-identified by trained experts, and
>>often rely on data that may not be
>> available in visible photos (soil types, historical use records,
>>infrared bands), or obvious without training
>> (vegetation types).
>That may be so, where my only experience with these places is "I used
>to play there when I was a kid"- and I look at the Bing imagery and it
>looks like I remember.
>> While I won't argue that these are 100% "objective" (simply because I
>>doubt there is any such thing),
>>"subjective" is not the same as wrong, and there are often good reasons
>>to trust one person's "subjective"
>> opinion over another's.
>That is not a view that jives with the OSM philosophy. If two OSM
>observes look at an area, they should be able to come to roughly the
>same conclusions. Additionally, they do not need to be experts, as we
>do not have such requirements in the project.
>The arguments you put forward are exactly one of the arguments why
>some of us do not believe that landuse is a generally good thing to
>store in OSM generally, because its so difficult to measure by
>>> I think that unlike the TIGER work that's being proposed, this import
>>> is not really fixable. In order to fix it, the relations and their
>>> component ways would basically need to be reconstructed. The work
>>> would be huge and so complex I don't think that it would be doable
>>> without some serious software engineering.
>> I'm skeptical of this statement, though I will admit to not having
>>looked closely at the data.
>>> So my proposal is to remove this import entirely.
>> My preference is to fix, rather than to remove.
>Darrell, what is your OSM username? I ask because I've done quite a
>lot of fixing of New Jersey, and especially trying to fix the import,
>and these conclusions come from about a year of trying to fix it (off
>and on).
>If someone with 4+ years of active contributions, deep involvement
>with the OSM technical community etc. can't figure out how to unwind
>the complex data structures easily in order to fix small problems,
>then I have a lot less hope for someone who is new to the project, or
>even your average casual mapper.
>From the tone of your email, I'm guessing that you feel passionately
>about this topic. Perhaps you can find solutions to the various
>problems. If that's the case, then I look forward to reading your
>proposal on what to do with the import.
>- Serge
>Imports-us mailing list
>Imports-us at openstreetmap.org

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