[Talk-ca] Aylmer/Hull QC: CanVec import overwriting existing edits

[Adam Dunn]

This is exactly why it's important to get more local people importing
Canvec. If we can get people some experience by playing around in a
sandbox (ie. they get to try out connecting intersections, editing
relations, etc, without saving), and when they have some editing
practice, then let them import Canvec for their local area, we will
see less of these types of problems. When four or five people are
trying to import all of Canada, that's where problems arise. Sometimes
when trying to import an area we are not familiar with, we try to
guess which source of data is more accurate, and we guess wrong. I've
seen cases in BC where somebody has made many edits that are
*obviously* wrong, and after a while I start to assume that *any* edit
by that person is of low quality. Canvec is generally very good, so
sometimes it's easy to think that it's the most up-to-date. This
doesn't excuse deleting traffic lights or changing street
classification, but could be a fair assumption when Bing shows a road
under construction and Canvec has it completed. Bing imagery for
Chilliwack has an empty field where Mr. Mikes restaurant has been
standing for five or six years (the Bing imagery was actually taken in
2003), while Canvec has a new road that was built two summers ago. And
this is a city of ~60k people in the Fraser Valley near the US border,
so we usually have up-to-date aerial imagery. It's difficult to guess
the accuracy of pre-existing data, or what source was used, and how
old the source was at the time (GPS? Yahoo? Bing? Landsat? Yes I've
seen highway traces done from Landsat).

You can check how old Bing imagery is for any area using
[http://mvexel.dev.openstreetmap.org/bing/] Aylmer was photographed in
the summer of 2006.

I once calculated that if one person were to do one Canvec subtile
(092H04.0.0) per day (about half an hour of work per day, depending on
pre-existing data), it would take ~360 years to complete the Canvec
import. Don't wait for someone else to import: get your friends
involved and have a mapping/import party for your local area!

Adam

On Sat, Feb 19, 2011 at 12:27 PM, Jonathan Crowe
<jonathan.crowe at gmail.com> wrote:
> This is rather discouraging and frustrating.
>
> When the Bing imagery was made available, I spent a fair amount of
> time cleaning up the maps in Aylmer, Quebec, a western suburb of
> Gatineau. Just discovered that my edits have been overwritten by
> another user importing CanVec data.
>
> This import has introduced hundreds of errors:
>
> - Proposed and under-construction streets are shown as completed.
> - Streets are tagged as unclassified.
> - Service roads have been removed altogether.
> - Turning circles and traffic signals are missing.
> - Certain streets do not line up with high-resolution Bing imagery,
> and not in an off-by-a-few-metres way -- for example, the Bing image
> has a subtle S-curve, the CanVec data has a rather crude straight line
> bisecting the curve.
>
> This means that Aylmer now needs dozens of person-hours to get it back
> to where it was -- and at this point I'm discouraged enough to say the
> hell with this project and find something better to do with my spare
> time.
>
> Much of Ottawa is in a similar state: manual edits superimposed with
> CanVec imports that may or may not have been more accurate, and now
> there are two or three duplicates on top of one another. It's a mess,
> and it's in no way ready for MapQuest.
>
> I thought CanVec imports were frowned upon when there was existing road data?
>
> I'll tell you this: this is not the way to encourage people to
> contribute, if all the work we do with imagery is subject to
> obliteration by someone else's work with government vector data.
>
> Yours in frustration,
>
> Jonathan Crowe
> The Map Room: A Weblog About Maps
> http://www.maproomblog.com/
>
> _______________________________________________
> Talk-ca mailing list
> Talk-ca at openstreetmap.org
> http://lists.openstreetmap.org/listinfo/talk-ca
>