[talk-au] Import vs filtering query
andrew.harvey4 at gmail.com
Mon Sep 6 01:44:24 UTC 2021
I also wouldn't consider this an import, because you're just using the data
to filter down potential issues which you then cross reference with other
On Sat, 4 Sept 2021 at 20:55, Little Maps <mapslittle at gmail.com> wrote:
> Hi all, my understanding is that the process described below is a big
> filtering exercise rather than a data import, but since I’ve never been
> involved in an import before, I’d like to check before progressing. Thanks
> in advance for your feedback.
> Goal: to update road surface tags across regional Victoria where
> necessary. Many surface tags were added 8-10 years ago and a surprising
> number of roads have been surfaced since then. (I’m only interested in
> sealed/paved vs unsealed/unpaved options, not subsets of these.)
> Method: compare road surface data in OSM against data in the Vic
> government’s transport dataset which we have permission and waiver to use.
> All rural roads from motorways to unclassified (not residential, service,
> etc) that have different tags in OSM and the gov dataset will be examined
> against satellite imagery and Mapillary, and any decisions on whether to
> update the surface tags will be made based solely on the imagery. No data
> will be directly copied from the gov dataset. Hence, as I understand osm’s
> import guidelines, this is a big filtering exercise rather than an import.
> Is that a correct interpretation? I’ve added a longer explanation below to
> help answer any questions.
> Basic assumptions: (1) I assume both datasets were made independently, as
> I’ve not seen any evidence that OSM surface tags were copied from the Vic
> data (or that the gov copied from OSM). (2) If the 2 independent datasets
> both indicate the same surface then I assume it is most likely to be
> correct. If they indicate different surfaces then one must be in error. At
> the outset, I have no idea how accurate the Vic gov dataset is, so I’m not
> assuming it is infallible (it’s definitely not; see comment below).
> Methods: for every road segment that has a different surface tag in the 2
> datasets, I’d inspect the road using available imagery, as is normally done
> when adding or updating a surface tag. Existing OSM tags will either be
> altered or retained, as required. There’s no ambiguity involved in updating
> a tag from unpaved to paved. It’s much less common to need to update a tag
> from paved to unpaved. Again, this will be done based on imagery,
> regardless of what the Vic data says.
> Some prelim observations: I’ve trialled the method in NW Vic, where the
> method works fine on longer road segments/ways. The approach would have to
> be restricted to ways > 1-2 km long, and short ways will be ignored. From
> an initial subset of about 50 roads > 5 km long in NW Vic, I found about
> 2/3 of the discrepancies between the 2 datasets did not warrant any change
> in OSM and about 1/3 did. The Vic gov data doesn’t seem to be as up-to-date
> as the imagery and isn’t by any means perfect. Regardless, the approach
> looks to be a very effective way to find out-of-date and inaccurate road
> surface data across the state.
> At this stage I don’t know how many ways will be examined or changed, as
> it will depend on the minimal length of road I inspect. I’m envisaging
> about 1000 at the max, and probably fewer.
> My guess is that, if the process was completed across Vic, then the
> surface data in OSM would be extremely accurate, and more accurate than in
> the Vic gov database. If I get through enough of it without going bonkers,
> I’m interesting in summarising the findings to show which discrepancies
> were most common, etc.
> So, back to the original question, is this process ok to pursue, given
> that the sole function of the gov dataset is to provide a filtering
> mechanism to identify roads to investigate, and all decisions will be made
> based on legally available imagery, not the gov data?
> Thanks very much for your feedback, Ian
> Talk-au mailing list
> Talk-au at openstreetmap.org
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