Jochen Topf wrote:
Another similar concern I have with layers is that of fragmentation of
>the data which currently is all in the one main layer. In the past
>there were some people asking for separate thematic layers like
>landuse (e.g. in order to not show them in their editor), and
>introducing a layer-system might likely lead to fullfilling this
>desire. I see this as a problem because landuse is strongly tied to
>other objects like streets, building lots, and other polygons (e.g.
>amenity, leisure, place-polygons) and moving or editing only part of
>this data will also lead to out-of-sync-geometry between layers (won't
>fit one over the other). To avoid this people would have to look at
>all layers, which in the end eliminates the benefits of separate
>layers.
Yes, this is the biggest concern I have with this approach, too. We need
to develop an idea what data should be in different layers and what data
shouldn't. And this has to be something the whole project has to agree on.
We don't want a situation where we have to known that to get landcover in
France you'll have to add the "corinne" layer, but in Germany, the landcover
is inside the main layer!
I'm seeing an interface to the raw data that automatically filters which objects
are passed to the outgoing data stream. Theoretically there is no reason that
the data FEEDING the filter could not be in separate databases. But
alternatively separate tables within the one database may allow the faster
access to 'layers' of data? Personally I don't see this as a particular reason
to be 'layering' data.
I've commented elsewhere on the 'out-of-sync' geometry problem between layers,
and some potential layers such as contours do lend themselves to being isolated
from other data? I'm not too worried about differences as I'm sure it can be
managed if essential, but the 'difference' may also be legitimate and pulling
that apart at the moment is an even more interesting problem.
--
Lester Caine - G8HFL
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