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 sources.
On Sat, 4 Sept 2021 at 20:55, Little Maps <[email protected]> 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 > [email protected] > https://lists.openstreetmap.org/listinfo/talk-au >
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