Tech Tip:  Using Voronoi regions to 'Find the nearest ...'
Presented at the Puget Sound MapInfo User Group March 4, 2003
John Schlosser, Schlosser Geographic Systems, Inc. (SGSI)
 
  Voronoi regions:
  arrow.gif (63 bytes) Overview
  arrow.gif (63 bytes) Why use Voronoi?
  arrow.gif (63 bytes) How To
  arrow.gif (63 bytes) FAQs
  arrow.gif (63 bytes) References
 

Overview: Voronoi regions

  • Named after Russian mathematician:  G. F. Voronoi (1868 - 1908)
  • Technical:
    Voronoi region =     Dirichlet tessellation = Thiessen polygon. 
  • Practical:  "proximal polygons".
    Starting with a set of points, create a region around each point containing the area closest to that point.
  • Example:  a puddle of bubbles
  • http://www.cs.cornell.edu/Info/People/chew/Delaunay.html
  
   

Why use Voronoi?

To make a region map out of points

Creating "areas of influence" maps

  • First approximation of areas to be assigned to field offices?
  • Creating rough trade areas?

Find the nearest site ...

  • Determine which unit or office is closest and should respond.
  • Ad or literature should cite which store as "your local branch".
  
    How to: Voronoi regions in MapInfo Pro 7

Step 1:  Set one layer  "Editable".

Step 2:  Select at least 3 points.

  • Consider placing and selecting points at the edge of the area to be partitioned.

Step 3:  Menu > Objects > Voronoi ...

Specify how transfer data from points to the regions:

Click "OK" to build the proximal regions:


 

 

  
    FAQs: Frequently Asked Questions

Objects > Voronoi  menu option grey-ed out

  • No point objects are selected or no layer is set to be Editable or both.

No Field Value dialog appears after launching the Voronoi menu

  • You have probably set the Cosmetic layer to be Editable, instead of a base table.  In this case, there is nothing MapInfo can do with the field attributes.
  
    References:

MapInfo documentation:

"Chapter 20: Geographic Analysis"
MapInfo 7.0 User Guide, pp. 412-413.

"Create Object As Voronoi ..." command description in
MapInfo 7.0 Supplement, page 162.

On the web:

General site:
http://www.voronoi.com
Fun java applet:
http://www.cs.cornell.edu/Info/People/chew/Delaunay.html

 

  
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> http://www.sgsisupport.com/
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> http://www.mapinfouser.com/

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