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Re: Area of spatial objects

From: Frans Knibbe <frans.knibbe@geodan.nl>
Date: Fri, 16 Nov 2018 15:52:07 +0100
Message-ID: <CAFVDz43S9GG=9a3GVL459SuYLH90rGKbx1wEe9y7S3RVUCgp8g@mail.gmail.com>
To: Rob Atkinson <rob@metalinkage.com.au>
Cc: public-sdwig@w3.org
Yes, I think area would be a good thing to have in a general spatial
ontology. Just like length, perimeter, etc. To have those properties within
the scope of a spatial ontology would give a data publisher the option to
be clear about the nature of the thing the property belongs to: is it a
spatial object or the geometric representation of a spatial object?

As for addresses, we have a vocabulary for those: locn
<https://www.w3.org/ns/locn#>. It can be used to link an address to a
geometry. Then to specify the spatial nature of the related location just a
few special types of geometry seem to be needed: centroid, interior central
point and entry/exit point. A general spatial ontology could help with
those.

There are probably a lot of interesting use cases to think of, should
development of a spatial ontology take place and should that development
take the route of starting with collecting use cases.

I do think the topics of precision and accuracy apply to all kinds of
numerical data, not just spatial data.

Regards,
Frans



Op wo 14 nov. 2018 om 22:11 schreef Rob Atkinson <rob@metalinkage.com.au>:

> 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 Friday, 16 November 2018 14:52:42 UTC

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