[Talk-ca] What we dont know from GeoBase
Michael.Mepham at NRCan-RNCan.gc.ca
Mon Jan 5 22:34:51 GMT 2009
I will try to take this opportunity to address some of the issues raised
over the last couple of weeks. First off though - I hope everybody had
a good holiday and is starting out on a great new year.
I can confidently tell you that GeoBase will not be creating a nodes
only data set for the use of OSM. We have our hands full enough
completing and maintaining the existing data and adding new themes of
data, including the hydrographic data. If the discussion concludes that
nodes are desirable then the group will need to extract them themselves.
As a side note - the general policy is not to perform customisation on
the data for individual clients or client groups.
Road Names and Addresses
The objective is to have all the road names and address ranges for
Canada in GeoBase. There are a couple of things that need to be
understood in the scheduling of this. First is that adding this
information requires the agreement of the 14 governments involved and in
many cases agreements between the provincial and municipal governments
for a province. We expect to have a schedule in a few months, as we
work our way through the agreements.
Secondly, the data does not exist in some areas or even provinces. Or
it exists but is not available for free and unrestricted distribution.
One of the principles of GeoBase is that coverage is to be national. We
cannot just cherry pick the areas where data is easy but ignore the hard
Thirdly, accuracy is important. This data will not just be used for
pizza delivery but also for emergency services delivery as well as by
Statistics Canada and Elections Canada for delivery of their programs.
One Segment vs. Two Segments
A couple of posts have mentioned that for some reason the GeoBase data
has two segments for the same road, or part of a road. The answer to
that one is easy - there is a median or divider for that portion of the
road. (Note that short medians are not modelled into the data.)
Statistics Canada data
In evaluating the use of the Statistics Canada data sets I suggest that
you remember that they were developed for the specific purpose of census
taking and electoral boundary development. These applications require
far less positional accuracy than you may be expecting. Also, the
update cycle is tied to the 5 year census cycle.
OSM data vs. GeoBase data
I note with interest the discussions about whether or not to "replace"
existing OSM data with GeoBase data where the two coincide. The
discussion seems to recognise two options - replace the OSM or leave out
the GeoBase where there is duplication. I would like to suggest that
there is a third alternative that I have seen only hinted at so far and
that is to merge the two. Each data set has its own strengths and if
they were to be merged based on the strengths a superior data set could
result. OSM has attribution and linked data that exceeds what GeoBase
has or was designed to hold. GeoBase has a positional accuracy that
exceeds what most of the OSM data could achieve. It also has a set of
basic attributes based on national definitions and standards.
I realise that there is a reluctance to lose the valuable work of
volunteers but the objective of the overall project must be kept in the
forefront. And if I read the posts correctly the objective is still to
be decided and agreed on.
It is our experience that creating a data set is the easier part of the
project. Keeping the data current and correct is harder but
paradoxically cheaper than the original mapping. Of the millions of
kilometres of roads in Canada only a tiny percentage need to
changed/added/deleted as part of maintenance. The challenge is
identifying these roads. Any thoughts or suggestions from the members
of this list would be welcome. We are always trying to find more
economical methods for keeping the data current.
Also - there has been some discussion about the need to re-load the OSM
when there is a GeoBase update. I would point out that GeoBase has
begun issuing change files that reflect only what has changed between
two releases and that should simplify keeping the OSM current.
Natural Resources Canada
E-Mail: MMepham at NRCan.gc.ca <mailto:MMepham at NRCan.gc.ca>
06Ath Floor, Room. 646R
615 Booth Street
Ottawa, ON Canada K1A 0E9
100 Central Park Place
2208 Scarth Street
Regina, SK Canada S4P 2J6
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