[OSM-talk] OSM needs a measure for completeness

[Chris Morley]

David Earl wrote:
 > I've said before and I'll say again: we need a way of
 > asserting "this area is complete" (for one or more
 > definitions of completeness).

Andy Robinson (blackadder) wrote:
 > The only way that we are going to individually or
 > collectively state the completeness of a specific area
 > is to carry out a verification process. It doesn't have
 > to be done by third parties or even different contributors
 > but it does need to be done by someone.
 > We need a simple tag to display verification, perhaps
 > the username and a date, say verification=blackadder_20080111
 > or similar.

Martin Trautmann wrote:
 > Is OSM that far that we need verification and quality ensurance?
 > We are still far from completeness, which might be a primary goal.

I have started a new thread with a measure for completeness in the title 
because this is an important topic for OSM. But the response to the 
recent posts quoted above, and my raising of it last July, has been only 
luke-warm.

I wonder whether this is because "completeness" is associated in 
people's minds too closely with verification. As Andy has describes it 
in the (incomplete) quote above, verification involves individual 
accountability - "I personally accept responsibility for the accuracy of 
this data". I don't think this is suitable for OSM at the moment; it may 
be necessary in the future if and when OSM becomes a serious alternative 
to commercial suppliers - but not yet. I, and probably others, are eager 
to make their contributions of as high quality as possible, but are wary 
about making a public and personal commitment to their accuracy.

As is the case for all other mapping information, an assertion of 
completeness should only imply the best endeavours of the contributor, 
not a guarantee of 100% correctness. If you have ridden round a housing 
estate systematically and collected all the required information, you 
can reasonably say the area covered is complete. With this 
understanding, completeness would become part of routine mapping. It 
would encourage a systematic approach and the collection of any missed 
information.

A possible detailed approach is as follows. A completeness boundary 
would be modelled on coastline: it would enclose an area, but would 
consist of many (ordinary) ways, with the completed area on the right. 
They would be tagged with one (or possibly more) definitions of 
completeness like "major roads", "public roads", "public paths", which 
would be defined on a wiki page. Boundary ways would be moved or added 
on a day-to-day basis by anybody with local knowledge. An area might 
even have holes in it.  Somebody would provide an overview map showing 
completed areas, and its animation would feature in most presentations 
on OSM.

OSM really needs a measure for local completeness to demonstrate its 
progress externally. I hope enough people can be roused to discuss, and 
hopefully agree, the principles, before deciding on an implementation.

Chris