Convex Hull limitations?

[Iain Scott]

I have a large number of address points grouped by postcode, and I would like to to have a boundary around each of the individual postcode areas. 

My plan was to use the "Combine by column" function to group the address points and give me a multi-point object for each post code. Then to use the "Convex Hull" and the "create one output object for each input object" option to create a boundary around each postcode object. (finally, I would do a buffer to make the boundary a bit prettier). And indeed, this seems to work with one (or a few) post code(s) at a time, but when I select more than [a few] postcode objects to create the "Convex Hull", the "one output per input" option is greyed-out... 

Any thoughts on a better way of doing this process, or anyway around what I am guessing is a mapinfo "this operation is too complex" limitation? I suppose one could automate the process in order to do one convex hull at a time using mapbasic, but I'm not particularly confident using that... has anyone done this before and have an mbx to share?

regards,

Iain

[Bill Thoen]

Have you considered using a Voronoi diagram for this? This would be
simpler and would also give you a layer of convex areas with no gaps
between them. I suppose the question of how do you define the center
points of the post codes needs answering, but a simple (maybe too
simple) solution would be to select the average centroidX and centroidY
grouped by post code. The problem with using buffers and multi-point
objects is that you're making the problem more difficult than it needs
to be.

- Bill Thoen

[CDR Group]

Hi Iain

 

UK postcodes?

Acquire the postcode unit polygon dataset - would be the easiest route!

 

John Ievers

CDR Group
www.cdrgroup.co.uk
www.browse-a-map.co.uk
Tel: 01433 621282
Fax: 01433 621292
Specialists in Geographic Information Systems

CDR Group is the trading name of Contract Data Research Ltd.
Registered address Eccles House, Eccles Lane, Hope, Hope Valley, S33 6RW.
Registration No. 1972326
VAT No. GB373 3117 67

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[Iain Scott]

Ah. Yes. That would be easiest, wouldn't it? Well, that saves me an awful lot of work, thank you!

Iain