[Talk-ca] New user adding data, not sure what to do

Frank Steggink steggink at steggink.org
Sat Sep 12 01:19:19 BST 2009


Hi list,

I just _knew_ it would happen. As soon as I would start the Geobase 
import, some user would step up, and start adding data to the areas I'm 
about to import. And this is exactly what happened. To my surprise I 
discovered a whole lot of data southeast of Quebec City, in the 
Chaudière-Appalaches region: [1]. These are the NTS tiles 021L09, 10, 
15, and 16.

At first I was happy that there was some considerable activity in the 
Quebec region, other than my own. After examining the data, it comes 
from a user (Robert66) who has only joined us on Monday. Unfortunately 
this shines through his data as well: most of his roads are not 
connected, so that would involve a lot of cleanup. Apparently he had a 
blast this week: many small towns and villages were added. The data even 
has street names! See for example Montmagny: [2]. So, I've contacted him 
yesterday, in order to ask for more information. I haven't received a 
reply yet, but one day isn't that much.

Because this area was on my todo list, I decided to continue with my 
import. Tile 021L10 ([3]) is on tonight's program. After the data was 
loaded, I noticed a concentration of roads in St. Damien [4], which I 
didn't see yesterday. Apparently Robert66 was busy adding it today, see 
changeset 2451637. When zooming in, I noticed that, while the data 
looked topologically correct (apart from the fact that the roads aren't 
connected), many roads are displaced, up to 150 m, compared to the 
Geobase data. See [5], screenshot of OpenJump. Brown=OSM, green=Geobase. 
I know that Geobase isn't the most accurate dataset, but in the area I 
have imported data, it generally matched my roads reasonably well. The 
differences are up to 30 meters, although there are some exceptions. An 
example is the main road in the St. Damien screenshot, going from SW to 
NE. It was originally added by me, nearly a year ago: [6], as well as a 
few residential roads.

What I would like to know is: does anyone of you have a reasonable 
explanation as to how Robert66 has added his data? He has used Potlatch, 
and for that area there are no detailed Yahoo images. There is only one 
GPS trace of the main road. (It isn't mine: I'm using them only as a 
backdrop in JOSM.) I really hope he hasn't drawn the roads from memory, 
or some sketches, without the help of any GPS. Although I have traced 
only a few roads in St. Damien, I find it pretty odd that the roads I 
added myself are matching Geobase well, but the roads added by Robert66, 
are off up to 150 m!

My hands are actually itching to override his data, and only reuse the 
names, but that isn't really in the spirit of the import. I also don't 
think that would be wise, because there is no clarity about how he got 
the data. I think I'll go visit St. Damien this weekend, and do my own 
survey. If I find out that Robert66's additions are indeed way off as 
the OpenJump screenshot implies, then I'll probably replace his roads. 
I'll wait for an answer from him first. Maybe he can use a bit of 
education :)

As for my import, when I was writing this e-mail, I've uploaded the data 
from the standalone file, with bridges copied over, and some small 
corrections. See changeset 2452632. I've left out the residential roads 
in St. Damien. (Sam: there is even a note in your spreadsheet :) ) I'll 
cleanup the data, except for the St. Damien area. I'll follow a similar 
procedure for the rest of this entire area. Depending on the answer 
Robert66 can give me, I'll either leave his data in place, or add more 
Geobase roads, or eventually I'll survey those towns myself (which will 
be a lot of work).

So, what do you think? Do you have any additional suggestions as how to 
handle this situation?

Regards,

Frank

[1] 
http://www.openstreetmap.org/index.html?minlat=46.5&minlon=-71&maxlat=47&maxlon=-70&box=yes&layers=B000FTF
[2] http://osm.org/go/cKbzIEER--
[3] 
http://www.openstreetmap.org/index.html?mlat=46.625&mlon=-70.75&minlat=46.5&minlon=-71&maxlat=46.75&maxlon=-70.5&box=yes&layers=B000FTF
[4] http://osm.org/go/cKawVZPY--
[5] http://www.steggink.org/temp/St_Damien_QC.png
[6] http://www.openstreetmap.org/browse/way/27080076/history





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