[Openstreetmap-dev] Node / line segment database statistics separation

[Tom Carden]

Andy Robinson wrote:
>
> I see your logic here. Its just that I know we have a lot of loose nodes out
> there so was surprised by the difference. But if zero length segments is the
> reason then that could be the cause.
>   

Think about a basic grid (draw dots on paper).

In a 2x2 grid street pattern, there are 4 nodes and 4 lines, right?  But 
in a 3x3 there are 9 and 12, and in a 4x4 there are 16 and 24, and so 
on.  For n x n, there are n^2 nodes and (2n^2 - 2n) lines.  I think.  
Anyway, they diverge :)  This effect is lessened by orphan nodes and by 
long roads and other sections of the map that aren't pure grids, but 
then it's increased by things like 5 way junctions.  So you shouldn't be 
surprised to see more lines than nodes, you should be expecting it :)

Best,

Tom.