Hoi Mappers,
often we receive answers in which very inspiring examples of the
utilisation of Vertical mapper. Is there somewhere in the world an
inspiration book for sale? Where can I find interesting examples on
websites.
Dr Robert F. Dekker
Rotterdam Schoolboard
----- Original Message -----
From: Ole Gregor <[EMAIL PROTECTED]>
To: 'Jacques Paris' <[EMAIL PROTECTED]>; Reid Melanie
<[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Sent: Tuesday, June 01, 1999 8:44 PM
Subject: RE: MI Overlay Tools
> Hi
>
> I agree with Jacques, but there is a third solution - it's to use the
raster
> posibillities in Vertical Mapper, which can deal with fairly large grids
(a
> more sofisticated cell structure) and can make dynamic buffers (a grid
where
> the cell value tells about the distance to other objecvts). In the last
> months, I have both made a distance grid (25 m resoultion covering aprox.
> 7500 sqr km) and a site evaluation (new town development areas (250 m
> resolution, because I'm interested in a site which are at least 10
hectares
> and covering aprox 5000 sqr km). The hardest task was not the calculations
> but to figure out which parameters to use and their relative weigth.
>
> Ole Gregor, Viborg Amt (County), Denmark
> [EMAIL PROTECTED] TLF. (+45) 87271307
>
> > -----Original Message-----
> > From: Jacques Paris [SMTP:[EMAIL PROTECTED]]
> > Sent: Tuesday, June 01, 1999 1:59 PM
> > To: Reid Melanie; [EMAIL PROTECTED]
> > Subject: RE: MI Overlay Tools
> >
> > > -----Original Message-----
> > > [mailto:[EMAIL PROTECTED]]On Behalf Of Reid Melanie
> > ...
> > > ERSIS GIS Toolbox that appears in the Overlay Tools ?
> > > This .mbx creates a new table as a result of a merge of adjacent
> > objects
> > > with a common attribute in a specified field (combining adjacent
regions
> > > based on a common field). I have used this .mbx on a large dataset
and
> > > found that it creates slivers where some of the polygons join.
Therefore
> > > rigourous checking has to be done .
> > >
> > Melanie,
> >
> > I have a particular bad relationship with "slivers" that can create
havoc
> > in
> > some map manipulations, compounded when there are several layers of
> > overlays. But what can we do about it?
> >
> > One way is to redraw the maps to be overlaid onto some set of "common"
> > borders; that is one of the Robert's implied recommendations : "clean up
> > your data". Fair enough if some common border basis can be imagined;
fair
> > enough to expect that common segments be drawn exactly onto each other.
> >
> > But unfair in my eyes to the basic idea of overalying maps because one
> > should be able to do such operation without heavily redrawing. When
> > overlaying, one has to contend most often with maps coming from
different
> > sources, drawn with different objectives in mind. There is no reason to
> > prevent poorly fitted maps. I had to abandon any hope of even
> > demonstrating
> > the procedure for site potential evaluation using several layers of data
> > because of the constraints on the quality of the basic maps as a set.
> >
> > We see there an example of the duality geographer/cartographer,
> > analyst/programmer. Tell me what to do and I may find a way to do it.
> > Right
> > now, MI offers a very strict geometrical way to do thing (the overlay
> > function), but it is not satisfying to the user. Can you as a user tell
me
> > how to deal with slivers? How would you go to decide if they have to be
> > merged and to which region should they be reunited?
> >
> > I followed two paths in the past. One was to consider recoding the
> > resulting
> > regions; each resulting region carries the data of both original regions
> > to
> > which it belongs. Usually, one would map one variable from each data
set;
> > if
> > one recodifies combinations of data values, he can use these new codes
as
> > a
> > way to recombine disaggregated regions; maybe many slivers would then
> > disappear. But this is good only for a bivariate simple situation.
> >
> > The other approach, valid for any number of variables, is to forget
> > completely about the overlay technique and to use what I have called
> > "cellmaps". Generate a grid of cells and fill them with any kind of data
> > extracted from the base maps. I have documented this technique with all
> > its
> > pitfalls in CELLMAP.doc that you can download from our site if you go to
> > the
> > CELLMAB.zip or CELLMAP.zip topics. With it there is no sliver problem,
the
> > entire "worry" is the assignation of data values to each cell. Shifting
> > the
> > pain from place, no doubt, but opening the way to multivariate analysis
> > that
> > MI is unable to provide on its own.
> >
> > Quoting Robert's answer "... Also the eternal error in overlaying
polygons
> > makes
> > this program flakey...", I would lay that issue to rest if you are using
> > version 5.5. I would say that just for that reason (the complete redraw
of
> > the object handling routines) it is worth upgrading to 5.5
> >
> > Besides Robert's suggestion of buffering original regions, I would
expect
> > some reactions from our friends from the fuzzy side!
> >
> > Your question about slivers raises some fundamental issues in that
domain
> > of
> > spatial analysis using overlays. I have been better at framing the
> > questions
> > than at finding the answers. Help is seriously needed.
> >
> > Jacques Paris
> > ============================================================
> > e-mail [EMAIL PROTECTED]
> > alternate [EMAIL PROTECTED]
> >
> > gis activity (MapInfo mainly)
> > http://www.total.net/~rparis/gisproducts.htm
> > ============================================================
> >
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