[OSM-talk] Extract a polygon into a polygon filter file format

[Frederik Ramm]

Hi,

Phil! Gold wrote:
> Why is this so logical?  The exact same data can be derived from the
> intersection of the sets of elements in the two countries' (single-level)
> border relations.  

Put yourself in the position of having to create or maintain them.

Creation:

Cascading relations: You create ONE relation that contains all the ways 
making up the border between A and B (finding them is a cumbersome 
manual process). Then you create two relations for the two countries, 
each time adding only 4 or 5 sub-relations.

Single-relation approach: You create TWO relations that each contain all 
the ways making up the border between A and B (plus a lot more).

Maintenance:

Cascading: You split a way on the border between A and B. The newly 
created way is added to one relatively small relation and that's it.

Single-relation: The newly created way has to be added to two very large 
relations which you will have to first download and later upload as a 
whole.

Single-relation also has the higher risk of edit conflicts.

> It seems to me that because both shcmes can satisfy the
> use case, the preferable approace would be the simpler one, which I see as
> being the single-relation approach.

Simpler for reading, but, as explained above, more difficult/problematic 
for maintenance.

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"