[OSM-talk] open question about boundaries sharing nodes with ways or nodes

[Andrew Guertin]

On 10/14/2015 04:05 AM, Sebastiaan Couwenberg wrote:
> On 14-10-15 09:49, Badita Florin wrote:
>> Our task is to delete all the existing admin_level=6 boundaries and start
>> fresh, but this seems much more things needs to happen before you do this.
>
> Don't delete the existing boundaries, update them to match the new
> reality using the ReplaceGeometry feature in JOSM for example. When the
> data for shared nodes is available, it will disconnect the other ways
> from the boundary way being replaced leaving the other ways as they were.

I disagree with this suggestion, and I think the original plan of 
deleting the existing ways or tags and uploading new ones is better. 
Reasons:

1) The value of using Replace Geometry is very low for this case. The 
reason for doing so would be to make life easier for anyone who wants to 
know what OSM previously thought the boundaries are. Very few people 
will want to know that, especially since it won't provide any context 
for understanding the new, imported data. And for those few that ever 
will, the tools still exist and work fine.

2) Replace Geometry won't work well. To provide a meaningful consistency 
of history, there needs to be a roughly one-to-one correspondence 
between new objects and old.

To explain this with an example: Imagine the county boundaries are 
currently mapped, with one way between each pair of counties, and a 
relation for each county collecting the appropriate ways. Now add 
detail, mapping out the boundaries for each town. Each county relation 
is now formed by a larger number of smaller ways which are the town 
boundaries. What should happen to the original ways that were used for 
county boundaries? They don't correspond to anything in the new scheme, 
so there's nothing for Replace Geometry to do that makes sense.

--Andrew