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Re: Area of spatial objects

From: Rob Atkinson <rob@metalinkage.com.au>
Date: Thu, 15 Nov 2018 08:10:53 +1100
Message-ID: <CACfF9LwW2b7pOksTw7NVLEvmOX=RFtLo=8ZY3t68pEfzvSrmhg@mail.gmail.com>
To: Krzysztof Janowicz <janowicz@ucsb.edu>
Cc: Car Nicholas <Nicholas.Car@csiro.au>, Frans Knibbe <frans.knibbe@geodan.nl>, public-sdwig@w3.org
IMHO this is a candidate for discussion in the context of a general spatial
ontology.

There is an unhelpful proliferation of solutions to the semantics of the
relationships between objects/features and geometries in the Linked Data
world.

For example it common practice to have a point representing an address, but
that may semantically actually represent many possible things:
* centroid of dwelling
* centroid of land parcel
* centre of road frontage of land parcel/property
* actual entry point to property
* entry point to dwelling
* something unspecified

or for a city:  location of main post office, centroid of designated area,
centroid of observed area, etc. etc.  Same goes for an area - what is the
area of a city? many possible answers depending on semantic context.

and each geometry has a range of metadata - precision, accuracy, area

is area a property of a specific geometry, or a spatial attribute (again
with semantic qualification) of a thing.

On Tue, 13 Nov 2018 at 14:16, Krzysztof Janowicz <janowicz@ucsb.edu> wrote:

> On 11/7/18 4:54 AM, Car, Nicholas (L&W, Dutton Park) wrote:
>
> Hi Frans,
>
>
>
> What if I wanted to publish Features’ areas without also publishing
> geometries? What about features with a point geometry and an area, no
> polygon. Also, I have data where an area is given and also a polygon but I
> don’t know for sure if the area was calculated from the polygon. In fact I
> have data with an area and an Albers area and a geometry and don’t really
> know what happened to make which.
>
>
>
> So, I want to be able to represent area as a spatial property of a
> feature, independently of any geometry. For this I will try using
> Observations and Measurements-style mechanics for this.
>
>
>
> I think I might use subclassing of a sosa:ObservableProperty (
> https://www.w3.org/TR/vocab-ssn/#SOSAObservableProperty) to express
> spatial properties such as area and then relate then to a geo:Feature which
> would also, by SOSA logic, be a sosa:FeatureOfInterest. I may invent
> modelling to relate that spatial property to a geometry, but this wouldn’t
> be required, just nice to have if known.
>
>
> Yes, you would subclass sosa:ObservableProperty. Just as a tiny note, and
> sorry for being overly picky, there is a certain risk with properties such
> as area in conjunction with geometries, namely that the are not in sync. In
> fact, we published a paper that shows that this happens in many, if not in
> most, cases. Of course, you could argue that the defined area is the
> 'correct' observation and the area computed from a geometry just some
> approximation but it is worth keeping this in mind as we have no
> uncertainty model linked to sosa.
>
>
> Cheers,
>
> Jano
>
>
>
>
> Cheers,
>
>
>
> Nick
>
>
>
> *From:* Frans Knibbe <frans.knibbe@geodan.nl> <frans.knibbe@geodan.nl>
> *Sent:* Monday, 5 November 2018 6:22 PM
> *To:* public-sdwig@w3.org
> *Subject:* Re: Area of spatial objects
>
>
>
> Hi Nick,
>
>
>
> I wonder: Doesn't the fact that multiple areas for a single spatial thing
> are published mean that the areas are calculated from different geometric
> representations of that spatial thing? That would logically make the area a
> property of a geometry. Besides, the geometry instance could be used to
> link to the CRS (e.g. Albers), ideally by URI.
>
>
>
> CRS data linked to a geometry could also give access to the basic unit of
> the CRS (e.g. meter) and through that provide information on the units of
> properties derived from the geometry (like the area), but that would demand
> a fair amount of reasoning on the part of the data consumer.
>
>
>
> Regards,
>
> Frans
>
>
>
>
> --
> Krzysztof Janowicz
>
> Geography Department, University of California, Santa Barbara
> 4830 Ellison Hall, Santa Barbara, CA 93106-4060
>
> Email: jano@geog.ucsb.edu
> Webpage: http://geog.ucsb.edu/~jano/
> Semantic Web Journal: http://www.semantic-web-journal.net
>
>
Received on Wednesday, 14 November 2018 21:11:41 UTC

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