[OSM-dev] Interpreting segments of a way

[lars]

Etienne wrote:

> Ways are *ordered* lists of segments.

Few things can cause so much confusion as the word "ordered", and 
just reiterating or emphasizing the word doesn't clarify anything.
The key is the "who" question: ordered by whom?

Does it mean segments can only be added in order (ordered by the 
server), or does it mean that the server preserves whichever order 
the user prefers (ordered by the user)?

The latter is in fact the case.  The OSM server software lets 
users define (and redefine) ways as a sequence of any line 
segments, connected or not.  A "way" could consist of one line 
segment in Europe followed by one in America and one in Asia. The 
server doesn't enforce any proximity or ordering, but returns the 
same bunch of line segments in the same order as the way was 
defined. The database currently contains plenty of ways that are 
just a bunch of "unordered" line segments.


-- 
  Lars Aronsson (lars at aronsson.se)
  Aronsson Datateknik - http://aronsson.se