Here's an easy example. I just drew an hourglass figure in MapInfo pro with
a width and height of 80 miles. This hourglass was drawn in one "stroke" as
a "bow tie". It should have calculated an area of 3,200 square miles -- it
actually shows LESS THAN 1/2 SQUARE MILE in area.
This is because MapInfo looks at overlapping polygons in the same region
(collection of objects) as a cut-out. For instance, a polygon drawn within
another polygon is interpreted as a lake or whatever. When you have
self-intersecting polygons, the system is confused about what is true area.
You can still click in either side of this hourglass figure and get the
right values; however, anything you do with area computations on these
spatial analogies will be quite erroneous.
Steve E. Wallace
GIS & Market Information Manager
Florida Farm Bureau Insurance Companies
----- Original Message -----
From: Jose Marcos <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Friday, October 29, 1999 5:00 PM
Subject: MI topology question
> Hi,
>
> I've read about topology errors making the spatial aspect of the data
inaccurate. I'd like to know about how these errors can really mess up the
data. Can someone give me real examples on how these double nodes and self
intersecting polygons have interfered with their work? I need to explain to
my manager why these errors need to be cleaned up. Thanks.
>
> jose
>
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