[OSM-talk] Multiple Layers for OSM

Martin Koppenhoefer dieterdreist at gmail.com
Mon Sep 24 10:35:45 BST 2012


2012/9/24 Jochen Topf <jochen at remote.org>:
> http://blog.jochentopf.com/2012-09-23-multiple-layers-for-osm.html
> If anybody wants to comment, I think this mailing list is the right place.


IMHO there are different requirements for these layers according to
what is on them and how it is related to the data on other layers.

E.g. the birds routes would not create much problems because they are
only roughly linked to current OSM-data, while for the historic data
layer I think it would be desirable to have that directly linked (or
at least a possibility to link it) to the current data. This is
important when there are remains of the historic objects  that are
still (also partly) present in the current world. These could be
either physical but also "conceptual" (e.g. parcels of a roman castrum
which are still valid for todays town, leading the streets (=voids) to
be where they used to be).
Other examples for this might be city walls, ruins and other remains
of historic buildings, historic walls, ...). The problem here is not
with static data but arises from the fact that our current OSM data is
in continuous motion: as soon as someone moves the current city wall
(or refines it) in order to improve it, the historic-layer city-walls
should also be refined (or they will get out of sync). We could maybe
have something like hardlinks on filesystems for OSM-objects
(nodes/way/relations) to solve this? In other cases it might not be
desirable that historic objects change when the current objects get
modified (i.e. this will also raise complexity a lot for the mapper,
as he will have to decide for his edits whether they should also be
applied to linked data, which is likely "specialist data").

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.

cheers,
Martin



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