[OSM-talk] Layers and landuse

[Lester Caine]

On 29/06/15 04:06, Warin wrote:
>>> If lower than the 'original ground level' then layer=-1 (or more)
>>
>> "layer" are tags to map relative local stacking (which object is above
>> which other object where they overlap), it has nothing to do with
>> original ground level. Where objects do not overlap, the tag is
>> meaningless.
>>
>>
> There should be a reference point, so that what one mapper maps can be
> verified by another mapper.
> 
> I use the 'original ground level' as that reference point and call it
> level 0.
> 
> If you used level 2 it would work ... but the next mapper could use
> level -2 .. and it would look rather strange .. especially if the two
> were linked .. the link would need to go from one level to the other..
> other wise the link would not be to teh correct layer/level. If both
> mappers use the same reference problems are reduced.

The problem with all of these is simply that OSM does not do height
which is a pity. I have several areas around here which are difficult to
map, and certainly can't be navigated too by a router simply because
'original ground level' is a couple of hundred feet difference from one
side to the other.

Example ... one enters the car park at level 1 ... it goes up in half
level steps to level 6 which is 'ground level' for the rest of Evesham.

Mellieha in Malta was even worse with entrances to car parks several
hundred feet above almost adjacent roads.

Landuse should be a 'virtual' layer, as should all 'political' concepts.
Keep 'layers' to at least keep the vertical structures sort of working
although it is now time that 'height' at least had some place!

What is the main problem here is the attempt to use the same way for
several unrelated elements. We know that the editors simply can't cope
with 'relations' and without a mechanism to provide duplicate ways where
one use needs splitting from another we are not going to be able to keep
the data consistent. Coastline is a goo example. If that was a set of
data on it's own 'PLANE' that could be viewed in isolation, then we
could modify the coastline and then simply flag what adjacent detail
then needs review ... coastal erosion etc.

Boundaries and landuse are another 'plane' independent of layer,
although 'mixed' use land may well be augmented by different tags once
the layers are better structured?

-- 
Lester Caine - G8HFL
-----------------------------
Contact - http://lsces.co.uk/wiki/?page=contact
L.S.Caine Electronic Services - http://lsces.co.uk
EnquirySolve - http://enquirysolve.com/
Model Engineers Digital Workshop - http://medw.co.uk
Rainbow Digital Media - http://rainbowdigitalmedia.co.uk