[R-sig-Geo] Colouring maps so that adjacent polygons differ in colour

Barry Rowlingson b.rowlingson at lancaster.ac.uk
Wed Apr 6 10:14:26 CEST 2011

On Wed, Apr 6, 2011 at 8:38 AM, Roger Bivand <Roger.Bivand at nhh.no> wrote:

> I've asked Barry off-list about this, there was a case a little while ago
> with unexpected results because of inserted sliver polygons causing
> apparently separate observations to be neighbours (the slivers were only
> visible when zooming right in). There are also differences in the way
> software may handle precision (snapping). More will follow ...

 Yes, I suspect its precision. poly2nb was showing two km-sized
regions as disconnected which were 0.01mm (yes, milimetres, about a
hair's breadth) apart. The rgeos functions had them as connected.

 If I get a chance today I'll investigate more.


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