[OSM-talk] OTG rule, borders & mountains existing | Re: Crimea situation - on the ground

Colin Smale colin.smale at xs4all.nl
Sun Feb 9 11:02:19 UTC 2020


On 2020-02-09 04:26, Joseph Eisenberg wrote:

>> Re: "on a government map, by legal / statutory decree, from data authoritatively published on a website"
> 
> These examples are not "good practice" sources for openstreetmap.
> While many mappers import data from such sources, there is no "value
> added" in the case that mappers are unable to confirm if the
> government or "authoritative" data is accurate or inaccurate. Since
> the data in Openstreetmap can be changed at any time, and often by
> mistakes caused by new mappers, the authoritative database or source
> will always be better for database users to consult directly, unless
> openstreetmap can improve the originally imported data by checking it
> against reality.

I beg to differ. Importing positions of accurately and authoritatively
surveyed objects gives us calibration points for our more manual work.
We are all warned about distortions and offsets in aerial imagery, and
99% of our on-the-ground mappers will be using consumer-grade GPS. If
the location of an admin boundary has been surveyed to centimetre
accuracy as lat X / lon Y, the presence of this in the OSM database,
plus an indication of its authoritative source, gives an invaluable
frame of reference. If Joe Bloggs comes along with his smartphone and
locates it at X+dX,Y+dY he needs to understand that it is he who has the
inferior data, and he should refrain from "improving" OSM by changing
the location of the boundary. If other objects like rivers, highways etc
should probably coincide with the admin boundary but don't, Joe Bloggs
needs to consider that the professionally surveyed data is more likely
to be correct before moving the admin boundary in OSM to fit his
imperfect data. 

Besides, OSM strives not only to be "complete" but also "useful". If
imports can increase the usefulness of OSM, it is likely to positively
impact its adoption. So what's not to like? 

A subject often ignored in OSM is defining what me mean by "data
quality." Quality is always relative to some definition of perfection.
Is a point entered by an "OTG mapper" with a smartphone, of higher
quality than a definitive, authoritative survey? 

> Remember, this is the "good practice" page we are talking about
> editing, not the "how things really are done" page: we want to focuse
> on the "Gold Standard", best practices.

Irrespective of the discussion above, Best Practises and Gold Standards
can often usefully be illustrated by negative examples. Standards have
quality too! A good standard will be unambiguous; one that is vague and
open to a lot of interpretation is not a good standard.
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