Fwd: Requirement for topological data?

Hello,

This is a message I intended to send to this group, but I just noticed I
sent it to another (non-existent, as far as I can tell) address.

Regards,
Frans

---------- Forwarded message ----------
From: Frans Knibbe <frans.knibbe@geodan.nl>
Date: 31 August 2016 at 14:28
Subject: Requirement for topological data?
To: "sdwwg@lists.opengeospatial.org" <SDWWG@lists.opengeospatial.org>


Hello all,

In general I do not like to assign myself more work, but I do wonder if
there is yet another requirement that we have forgotten to identify. It
could go something like this:

It should be possible to publish and use topological geometric data on the
web.

To be clear, I mean something else than the ability to assert topological
relationships between spatial things (e.g. A is contained by B) or to use
topological functions in queries (e.g. give me all geometries touching
geometry B). This is about maintaining the topological awareness in
geometric datasets, as supported by data stores like PostGIS
<http://postgis.net/docs/Topology.html> and Oracle Spatial
<https://docs.oracle.com/cd/B19306_01/appdev.102/b14256/sdo_topo_concepts.htm>.
As an example, a line geometry could be aware that it functions as a border
between two municipalities and as a border between two provinces. And the
line 'knows' which polygons are on its left and which polygons are on its
right, and to which other lines it is connected. GIS data stores can have
extended data models to deal with this extra level of information, next to
the bare geometry. An interchange format exists for topological geometric
data: TopoJSON <https://github.com/mbostock/topojson/wiki>.

I think that whatever standards or recommendations we come up with, working
with topological geometric data on the web should be possible and should at
least not be hampered in any way. So that is why it would be good to have
this extra requirement.

I stumbled upon the topic when I talked with a colleague about vector
tiling (publishing vector geometry as a pyramid of tiles, just like is done
with map images). For that to work, good generalization of geometry is
required and for good generalization topological awareness is required,
because in general you don't want generalisation to change topological
relationships.

More in general, generalisation of geometry is necessary for limiting the
bulk of geometry on the web and giving consumers the opportunity to request
or filter data with an appropriate level of detail. So that at least is
some sort of use case for the requirement.

Regards,
Frans