Arcplot Map & Page Scaling Settings

In response to the question:

>
>I have a question about the map composition.  After making a map composition,
>if I want to change only the pagesize, map scale, or other basic elements of 
>the map without changing, for example, the polygon shades, textfont, and line
>symbols, is it possible to modify the map without redoing the whole map
>composition?  How could it be done? We are thinking that we might have to
>change something in our modeling map composition after plotting the map.
>(The first map which is plotted would be our draft version.)
>I hope there is a short way to do it.
>

Is my response:

The various coverage-to-page-transformation environment settings -- pagesize,
mapextent, mapunits, mapscale, mapposition, maplimits -- can be changed but
you must understand their effects and the fact that map composition elements
(called by Arcplot "map elements") are stored in page units with no maintained
link to coverage units.  This takes a bit of getting used to, but is a
necessary part of working in the two coordinate systems.  The most important
effect is that once you've created composition graphic elements from coverage
features, if you change some of these environment settings any new graphic
elements created from coverage features may not fit to the previous elements.

Some guidelines to remember:

1. You can freely change these transformation environment settings once you've
finished putting coverage features into your map composition.  Your
composition now exists as an independent graphic entity, and you can move
elements around on the graphic page; you can even rescale your
coverage-derived or other map elements using commands like mfit.  Just don't
try to add any new coverage features that you hope to fit with pre-existing
elements.

2. You can of course set up new transformation environment settings to be used
in creating a second map on your page, e.g. an inset map.  This is one of the
reasons why you need to have these two environments -- map (coverage) and page
-- separate: with an inset you need to work with different scales on different
parts of the graphic page.  For this purpose you can use maplimits to set up
an inset area on the page, and set up a mapscale and possibly mapposition
appropriate for the inset.  If you're careful, you should be able to work
back-and-forth between you're two page areas.

3. Some transformation environment settings have more effect on the
transformation than others:
   - You would rarely change MAPUNITS of course, though you can certainly see
the effect of not using this setting (coverage units are then assumed to be in
inches!).  
   - If (and only if) mapposition is set to LL LL, PAGESIZE can usually be
modified without changing the transformation.  The only problem you might
encounter would be if you reduced the pagesize to an area smaller than your
mapextent or smaller than your pre-existing distribution of map composition
elements -- elements and coverage features extending outside of the new
pagesize will be clipped.
   - Unless you're creating an inset map, MAPEXTENT should never be changed.
It helps to determine the position of the coverage on the page, along with the
mapposition setting.  When you're first learning Arcplot, you learn that
mapextent is something to set before you can draw anything from a coverage.
Unfortunately this is somehow extended to the idea that mape must be set anew
for each coverage accessed.  This can produce some bizarre results.  Since
most of the coverages you're working with have the same map extent, setting
the mapextent anew for each coverage has no effect; it's only when you
superimpose coverages with different map extents (such as the results of your
overlays) that you see the effect: the scaling is the same, but the new
coverage element is shifted relative to the old ones.
   - MAPLIMITS and MAPPOSITION have no effect on scaling, but do (with
MAPEXTENT) determine the position of coverage features on the page, part of
the overall coverage-to-page transformation.
   - MAPSCALE has an obvious impact on the transformation.


I hope this clears up any confusion.

Jerry