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>Date: Thu, 24 Sep 1998 11:24:48 -0400
>From: Elaine Hallisey Hendrix <[log in to unmask]>
>Subject: Re: MM: Mapping on truly small and large scales (fwd)
 
 
> While we're at it, those of us who have become cartographers after starting
> out in other scientific or technical professions are almost invariably annoyed
> by the use of the expression "scale" to describe a map. On paper maps, this
> served a useful, immediate purpose. But the retention of this terminology for
> digital mapping products is almost meaningless. What does it mean to say that
> the DCW (etc.) mapping products are 1:1,000,000 scale? Even if you look at the
> details of the scanning method, the smallest features certainly do not
> correspond to the smallest features on high-quality paper maps scaled at
> 1-to-1million. Eventually, cartography will have to adopt the concept of
> resolution --a map's quality is defined by the smallest detail that it can
> faithfully resolve (or the smallest distance between neighboring items that it
> can distinguish separately). A map can be printed or reproduced at almost any
> linear scale today. But the resolution remains the same.
>
 
If you're talking about scanning a hardcopy paper map to create a digital image
of points, lines, and polygons for cartographic display only, then scale is
meaningless.
If you're using digital spatial data for analysis, however, you must know the
resolution
or scale at which the data, raster or vector, were originally obtained to
determine the level
of precision at which you can work.  For example, if you're studying historic
preservation
in Cairo, you'd prefer satellite imagery at a resolution of 1.56 m per cell over
imagery at
a resolution of 20 m.  You'd also prefer vector data (roads, building footprints,
etc.) at a
much larger scale than DCW 1:1,000,000.  Spatial data at the 1:100,000,000 scale
is just
not detailed enough for this type of study.  The analyst needs to know the
original scale/
resolution to build an acceptable digital database.
 
--
Elaine Hallisey Hendrix
GIS Research Coordinator
Department of Anthropology & Geography
Georgia State University
Phone:  (404) 651-1828    Email:  [log in to unmask]
Department Web Site:  http://www.gsu.edu/~wwwgeg
 
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