Re: [Talk-ca] Formal proposal to replace the existing Ottawa information with Geobase information.

[John Whelan]

If Ottawa had a crowd who had done a considerable amount of GPS based mapping then I would totally agree with you.  My sampling has been done with a hand held WAAS GPS unit used whilst walking, I am not comparing the original OSM roads to the Geobase data but to a hand held GPS unit.  The Geobase tagged data seems to have a much closer agreement with the GPS unit. I used to work for Statistics Canada and I did some work in quality control in industry so I am aware that my samples to verify what is there so far doesn't prove everything is bad unfortunately I am also aware that the probability of the rest of the data being dubious increases with every new error found. One concern comes from talking to people who are interested in trees in Ottawa.  They like the idea of taking a photograph with a time stamp on it so its GPS position can be determined then have a more knowledgeable person identify the tree more exactly.  The city centre looks like its about 30 meters out.  Currently I have identified a fire station being roughly 100 meters off.  One road was more than 100 meters off at one end, causing parts of other roads to be omitted on the import.  Are we saying the the tree people take your photo and the GPS coordinates put it on our map but accept that it might appear 100 meters away from its location?  I honestly don't think this data is based on a GPS trace. >If you are in the area that you are looking at the best, and really only, option is to check out the area yourself with a GPS and to correct any discrepancies regardless of if they were made by a individual mapper or as part of the GeoBase import.  It is possible to modify the data regardless of the source and doing so improves the map.  Replacing all of the user contributed data automatically with GeoBase data is not the answer and can even cause errors because the GeoBase data is not always the most current either.  So update, and correct, the data regardless of the source by physically checking it, preferably with a GPS. I agree with this statement as well however given the current known resources in Ottawa then I think it is better to go clean import from Geobase so we have a known quality of data then use groups such as the residents associations, the bus fanatics, the tree huggers whose primary interest may not be mapping to improve the result.  That way we end up with something usable quickly.  We are leveraging on the resources available.  However to leverage them I have to be able to say to them this is something useful for you today, not when we have done a GPS survey and corrected the map it will be useful.  Current known resources are one person who lives in the suburbs walking with a GPS unit and there are a lot of roads to cover.  I haven't come across a community of OSM mappers who party every week in Ottawa. To me OSM is not a printed map in the traditional sense but a GIS system which means the ability to add tags easily is very important. >The data contributed by all contributors should stay regardless of the apparent quality. The OpenStreetMap wiki about imports (http://wiki.openstreetmap.org/wiki/Bulk_Importing ) clearly states:   "Bulk imports are undertaken as a supplement to data collected by individual volunteers, and their data and ability to work in an area always has priority." which should be well regarded as a guideline for all of the imports in Canada and abroad.  They do not differentiate between good quality and poor quality work nor about the apparent quality of the imported data.  And the imported data varies in quality as well.  Some of it is very high quality Differential GPS but other areas are of a lower quality. I'm permitted to correct any data in an existing map, so "data contributed by all contributors should stay regardless of apparent quality" only means what I want it to mean. These are general guidelines drawn up in Europe where the ratio of GPS equipped mappers to road distance is quite reasonable.   Ottawa does not have the same resources and I think in this particular case we should look for a more appropriate solution.  I think the issue is a local one, I'm not asking for this for everywhere in Canada and I think the decision should be a local one.  So far I have not seen any input from some one doing OSM mapping in Ottawa. Cheerio John Gerald A wrote: Hi, On Wed, Oct 28, 2009 at 9:52 AM, john whelan <jwhelan0...@gmail.com> wrote: I accept that just because Geobase data is from the government it does not mean that is is 100% accurate but it is consistent.  Roads do connect which is important when putting together routing information. I'm not local  to Ottawa, so you can take this with a grain of salt. First, I have mapped some stuff in the Toronto area which was "adjusted" better with the Geobase data. It really discouraged me from participating, because why actually map when someone else will do it different "better" eventually? I think this goes against the crowdsource we draw upon. It's better to add where there are no maps, so you won't step on anyone's toes. Second, not all the data seems to be connected -- around here, hardly any of it was, making it entirely worthless for any purpose but casual observance on the slippy map. Further, consistent and wrong is still wrong, and I think we should try to produce a map that is correct, not "consistent". (And there is wrong bits in the import data). So, my suggestion would be import what we don't have, rather then trash what another mapper has worked on -- and be aware that the import might not be what you hope it is. It does move us forward, but we need people on the ground to verify and expand it. Thanks, Gerald.

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