[OSM-talk] Duplicate nodes generally

[Mike N.]

> What is the problem with duplicate nodes, exactly?

  The only time they are an actual problem is when the map data does not 
represent reality - when a roads cross in a physical intersection, but in 
OSM only have 2 nodes at the same location instead of a shared node, or a 
closed polygon in which separate starting and ending nodes are physically at 
the same point, rather than using a single common node per OSM convention. 
Other than that, some people have viewed duplicate node elimination as an 
effective way to minimize the planet size and have actually damaged the data 
by incorrect node merges.