485
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the ontology classes allowed for more flexibility than some of
the very specific NLUD classes.
Land Use was a much more complicated subject. The link
between the NLUD classification and the classes in the
ontology did not present major problems. However, when it
came to the actual classification using the data available there
were a high number of polygons with unknown land use. Also,
the diverse nature of land use meant that some polygons had
several potential numbers of uses which could complicate the
management and display of information for those using a
detailed classification. Granularity is therefore an issue.
There was a clear aid from aerial photography to distinguish
residential areas from other that could be categorised as
commercial or industrial buildings. It also helped to identify
uses such as hospitals or schools and verify some land covers
such as sand or scrub. However this assessment was done
manually. More research is needed to investigate the possibility
of an automatic way of identifying these areas.
3.3 Discussion and further work
The results from the trial in Bournemouth highlighted the
following issues:
- Need to asses other data sources. There are a few sources of
ancillary data that could help complement the information that
OS already hold. Some of them could come from directories
such as Thomson, Yell, Experian and Valuation Office. One of
the problems with these directories is that their information is
generally not georeferenced. A test matching some of these
directories to references on the ground achieved a 60% success.
However it proved to be very time consuming.
- Need to asses other methods of data capture, (i) Web
harvesting. We performed a trial on web harvesting to
complement and validate the information hold by Ordnance
Survey. The first obstacle are legal constrains on use of the
data which meant 80% of all sites could not be harvested.
Furthermore, it is usually difficult to find out the currency of
data provided in the web. The conclusion from this study was
that automatic web harvesting is not suitable for land cover and
land use information, (ii) Other sources of data capture to
consider are surveyors and video surveying. Surveyors are used
daily by Ordnance Survey to record changes in OS Mastermap
layers. We have to explore the way of taking advantage of this
resource so that they record land cover and land use information
at the same time. A video capture trial is planned for this
summer (iii) Automatic capture of land uses using aerial
photography. The main objective of this assessment would be to
determine what can be classified and in which way this
information could complement that collected through other
sources.
- Need for user feedback. We need to know whether this
approach answers any of the current of future land cover and
land use user’s needs and could be a way of integrating
different datasets.
In conclusion, the design of an object-oriented ontology
framework for land use and land cover that provides a high
level classification seems like the right approach in order to
provide a starting point and place of agreement for different
users. However, there is still a lot of work to do in terms of data
capture, data storage and maintenance, linkage with other
widely used classifications and the understanding of user needs.
References
Fonseca, F., Egenhofer, M., Davis Jr. C.A., Borges, K.A.V.
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ACKNOWLEDGEMENTS
I would like to thank Marion Seitz for her excellent work on
web harvesting during her time at Ordnance Survey.