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Posted by Paul Cooper on October 21, 2005, 3:52 pm
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wrote:
>Hello
>
> I am looking for a software that could help me to determine the zone
>covered by a zip or postal code. The input is the zip or postal code
>and the the software return an array of points. I could then trace a
>polygon from those point ans see the zone covered by the zip/postal
>code.
>
>Can I do this with a soft ? Which one?
>
>Thank you
>Martin
There are several techniques for constructing a polygon that surrounds
a cloud of points - the usual one is the convex hull, for which there
are several algorithms, all well represented on the web so a Google
search will find them. A lot of commercial software includes this,
often amongst the routines for handling DEM generation using
Triangulated Irregular Networks (TIN). There are more complex
algorithms around, but they are not widely implemented in commercial
software. Convex hulls suffer from the difficulty that they do not
follow "embayments" in the outline of the area.
There is, however, a philosophical point as to whether this is a good
thing to do! Your "postcode points" are seed points representing an
area. What that area is depends on the granularity of your data - it
could be an address (in which case, where is the point located within
the property concerned, what about flats and so on) or simply
centroids for larger areas whose geometry you don't know - for
example, streets, where a single postcode may cover a very complex
geometry. And, of course, as I have hinted, you may have quite an
irregular outline with embayments. Software to handle this case does
exist, but to set the parameters it requires you almost need to know
the required answer before you start.
I think you really want to think very hard about what you are trying
to do, and perhaps consider whether you are asking the right
questions.
Paul Cooper
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