[OSM-talk] Unmapped areas and map confidence

[Frederik Ramm]

Hi,

> These address one of my major concerns when I first joined OSM, that you had
> no idea of whether what you were looking at bore any relation to reality,
> especially if there was some information there. Of course, the map may lie,
> but usually it is simply just not finished, and very often it is known it is
> not finished and is being worked on.

In addition to what you're saying, it is also of interest to know as 
much as possible about the accuracy of data. If I drive along an already 
mapped road, twice, and find my track to be 10 metres south of what is 
mapped on each journey, then I tend to move the existing way - assuming 
it must have been done with older hardware or on a bad day. However if 
there was some tag telling me that the old way was professionally 
measured using full WAAS correction and aided by inertial navigation 
systems, then I'd probably stand back and leave the way alone ;-)

Also, consider the common situation where a road changes its name 
somewhere along the way. It is a huge difference whether someone says: 
"I stood at this place exactly and saw the roadsign posting 'Plumber 
Road' going north from here and 'Old Perth Road' going south" or if it 
is just "yeah, I saw a 'Plumber Road' sign here and an 'Old Perth Road' 
sign a bit later so the name change must be somewhere in between...".

Sometimes I use the source tag to confer a level of confidence (typical: 
"landuse=forest, source=landsat" to let people know that this is just a 
guess where there might be trees).

But all this is, strictly speaking, meta-information - not information 
about the world (which we store in our database), but information about 
our database (which we might store somewhere else). It is also, at least 
in the cases described by you, transient - dragons to be slain, not 
dragons to keep - in contrast to the data we collect about the world, 
which only changes if it gets corrected or if the world changes.

It may be worthwile to think about setting up something to - voluntarily 
- collect meta-information in. In addition to marking "here be dragons" 
areas or "looks strange on slippy map, someone please fix this" notes, 
people could also record their mapping tours there, maybe linking to an 
uploaded GPS track. This would also make it easy for people to find 
others mapping the same area and start talking to them.

I know that doesn't sound like the short-term solution you were looking 
for, David, but had so say it anyway ;-)

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'