[Tagging] Handle with care

[Greg Troxel]

Colin Smale <colin.smale at xs4all.nl> writes:

> 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"? 

There are changeset tags, yes.
And looking at

  https://wiki.openstreetmap.org/wiki/Massachusetts

one is directed to MassGIS imports

  https://wiki.openstreetmap.org/wiki/MassGIS

which as

  https://wiki.openstreetmap.org/wiki/MassGIS#Town_Boundaries_from_Survey_Points_Layer

which links to the state page about this.

> 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). 

When it isn't clear that what you're doing is an improvement, you should
message the other people involved.  In the Mass case, most of the active
mappers know each other.  Basically my point is that absent having a
good basis to know that what you're doing is an improvement, you should
be careful.  And a phone/hiking GPSr that shows within 10-20m is not
presumption that the new data is better.   If the phone GPS is showing
200m off, then yes, the existing data is bad.

I have actually written to people when I have tracks for hiking trails
in nearby towns that are off about 20m, to ask how they did it.  And
usually they say - "just my phone, feel free to fix".

And if you're not local, and definitely if you're not actually on the
ground, you should be extra careful.
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