| 7.2.4 Data
validation
Very few GIS products provide
valuable tools to facilitate the operations of checking the quality and
integrity of the digitised data and of the related attribute information.
This is quite surprising because governmental institutions invest a large
amount of time in attempting to evaluate the quality of data digitised
elsewhere. A few GIS do provide this checking mechanism, via user-programmable
rules. Besides of the detection and correction of topological errors, most
GIS software incorporate a limited number of functions for aiding the user
in identifying categorical errors in the input data. The problem becomes
crucial when such data have a large volume.
Under these circumstances, by
displaying the map along with spatially related terrain features, it may
be possible to detect and correct unrealistic or wrong associations of
different features.
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Click on the preview
in order to see a larger
version of this photo
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Two are the interesting
issues that can be seen in this picture. First, the handling of background
environment (here, vector data, symbolised by different colours). Second,
in terms of data validation, the identification of possible topological
errors: in these views, we highlighted (with yellow circles) the areas
on the current edit "coverage" (white vectors) that the GIS informs
us (by the small squares) that a line is open (not closed, not defining
a polygon). So we can examine if there are any unwanted overshoots, undershoots,
etc. & afterwards, we can correct them. |
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