Hi Brent, thanks for bringing up the oft-overlooked and even more often misunderstood confusion of accuracy over precision.
> Most (some? all?) of the CanVec data originally came from the > 1:50,000 NTS topographic maps . For clarity: which had their coordinates rounded off to the nearest metre (in UTM coordinate space), as per the NTDB specification. matt wilkie -------------------------------------------- Geographic Information, Information Management and Technology, Yukon Department of Environment 10 Burns Road * Whitehorse, Yukon * Y1A 4Y9 867-667-8133 Tel * 867-393-7003 Fax http://environmentyukon.gov.yk.ca/geomatics/ -------------------------------------------- Brent Fraser wrote: > I'm sure they mean accuracy instead of precision. Precision is just > the number of digits stored/displayed, whereas accuracy is how well > the data reflects reality. Just because you chose to display > coordinates to the nanometer doesn't mean they are that accurate. > Not that I want to confuse the issue, but it can be important. > > Most (some? all?) of the CanVec data originally came from the > 1:50,000 NTS topographic maps . Within the past few decades some > have been updated from medium-resolution satellite imagery, and some > have been updated with data from the various Provincial 1:20,000 > mapping initiatives. At any rate, the "Quantitative Horizontal > Accuracy Value" is given in the metadata for each NTS sheet, with a > number 30 meters being common. > > To stir the pot even more, the Manitoba government > (https://mli2.gov.mb.ca//) has it's 1:20k topographic maps available > for free (and the license looks libre too). Their metadata gives > accuracy values (Horizontal_Positional_Accuracy) of 1.25 meters, 2.5 > meters, etc. Wow! I expected 20 meters at best. > > And don't get me started on the accuracy of hand-held > navigation-grade GPS receivers... > > Best Regards, Brent Fraser > > > > > > Richard Weait wrote: >> Hi folks, >> >>> From the good folks at Natural Resources Canada (GeoBase). >> >> "Yes you can use the data found on GeoGratis site . The licences >> are identical. The only differences are the copyrights, one is >> GeoBase, the other one is NRCan (GeoGratis). >> >> Please note: The data found on GeoGratis could have different >> planimetric precision and could not fit exactly with the precise >> GeoBASe data or OSM data. Please refer to the metada info of the >> files you will be using." >> >> I'm sure that we are all excited about the additional data. Please >> note the guidance regarding precision. >> >> Best regards, Richard >> >> >> _______________________________________________ Talk-ca mailing >> list [email protected] >> http://lists.openstreetmap.org/listinfo/talk-ca >> > > _______________________________________________ Talk-ca mailing list > [email protected] > http://lists.openstreetmap.org/listinfo/talk-ca > _______________________________________________ Talk-ca mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk-ca
