# Re: Mapping question...

• Subject: Re: Mapping question...
• From: "James B Guthrie" <jim.guthrie(at)gov.edmonton.ab.ca>
• Date: Mon, 11 Jun 2001 13:56:55 -0600
• Newsgroups: comp.lang.idl-pvwave,sci.engr.surveying,comp.graphics.visualization
• Organization: University of Alberta, Edmonton, Canada
• References: <3b24e6b1@news.ColoState.EDU>
• Xref: news.doit.wisc.edu comp.lang.idl-pvwave:25302 sci.engr.surveying:31256 comp.graphics.visualization:17614

```Guillaume Dargaud wrote in message <3b24e6b1@news.ColoState.EDU>...>
>You end up with a tiny sahara, but large tropical zones...
>How would you go to do something like that...?
>I have seen it done before, but don't know what this kind of mapping is
>called.

It is called a cartogram. The population based one is called an
isodemographic map.
The manual form is accomplished by calculating a unit representation for the
smallest mappable entity. (Say 10,000 people). Then you create the shape
that encloses the largest number of entities in that unit for the map. (For
population in Canada, that would be metro Toronto). You give this the
"correct" shape enclosing the total area in units that it approximates. You
repeat the process for successively smaller reportable areas. Then you try
to fit the new maps in place relative to the first (largest) item. You may
find that you have to distort the  dimensions of smaller units that abut
larger ones. (So for example, Missasauga abuts Toronto in the expected
place). If you do that, then you have to reduce the perpendicular dimension
so that the area is unchanged, even though the shape is.
Repeat, working outward from the larger objects, and allowing for enclosure
in other "superior" shapes (say Ontario Province) which are also
proportionally sized and positions.
You might find an automated version of such mapping through a search on
"cartogram" or "cartograph".

-
>Guillaume Dargaud
>Colorado State University - Dept of Atmospheric Science
>http://rome.atmos.colostate.edu/

```