[talk-au] Import vs filtering query

Simon Poole simon at poole.ch
Sun Sep 5 09:30:46 UTC 2021


Hi

Your proposed workflow would seem to be totally OK to me and is clearly 
not an import. List the government data in the sources used in the 
changeset and IMHO you are good to go.

Simon

Am 04.09.2021 um 12:51 schrieb Little Maps:
>
> 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
>
>
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