I meant my question seriously, not hypothetically.... I assume all these boundary posts are tagged with something like "source:location=MA State Data Set 2015-01-19"? If not, how is a mapper to compare his "correctness" to the existing "correctness"?
Without this provenance information in the database, the accuracy is unknown to other mappers, and may in fact be worse (for example an armchair mapper digitising from small scale map). --colin On 2015-09-11 20:02, Greg Troxel wrote: > Colin Smale <colin.sm...@xs4all.nl> writes: > >> How does the chap with the GPS on his smartphone know that the old >> coordinate of 50.000 is "more correct" than his own measurement? > > This is generally a hard question, but if you're using a phone, and the > value you see is within 20m (or maybe 10m) of what's in the db, then you > shouldn't change it unless you've thought about why your new value is > better. And arguably data with higher-than-normal accuracy deserves a > note. > > Around me, town boundaries are defined by the actual positions of > granite markers. Massaschusetts publishes a dataset with coordinates > determined from a surveying long ago, reckoned forward to a modern > coordinate system. Those coordinates are in OSM. I've visited a number > of these, and of course my handheld GPS receiver gets different numbers. > But they are all close, and I have no reason to believe my measurements > are better. In fact, I think my measurements are worse. So I'm > certainly not changing the values in the database. > > So really, people just have to understand the expected errors of their > measurements.
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