Designing The Map; About Coordinate Systems - Autodesk 15606-011408-9330 - MAPGUIDE R6.3 SITE LIC-UPG R6 User Manual

Designing the Map

After you have planned the data and layers for your map, you need to address
design issues, such as which coordinate system to use, what precision you
want, and how to set up and use a design spreadsheet—as well as following
general design guidelines.

About Coordinate Systems

Mapping applications use coordinate systems to determine where to display
features on the map. In a latitude/longitude coordinate system, each coordi-
nate pair corresponds to an exact fixed location on the Earth; in an arbitrary
XY system, the coordinates have meaning in relation to each other but do
not necessarily correspond to exact fixed locations on the Earth.
For example, a floor plan map might specify that the southwest corner is 0,0
and the northeast corner is 500,500, so that if the building were moved to
another location, these coordinates would still be accurate because they are
not tied to exact locations on the Earth. If you used latitude/longitude coor-
dinates for that map, however, the coordinates would change if you moved
the building, because each pair corresponds to one exact point on the Earth.
Some types of arbitrary XY systems, such as the state plane coordinate
systems, make use of both of these concepts. Each coordinate system repre-
sents a specific area, usually a state or a section of a state. Within that area,
the coordinates are meaningful and represent exact locations on the Earth.
So a point with the coordinates 100000,100000 will always represent a
specific location in the New York state plane coordinate system. However, if
you change the coordinate system to another state plane coordinate system,
all of the data will move to that area, where 100000,100000 represents a
specific location in that area. In this way, the data is arbitrary XY, because the
numbers themselves do not represent exact locations except within the
context of the fixed areas.
Note that if you are using arbitrary XY data, it is not converted to lati-
tude/longitude, so you can use it only in maps that use arbitrary XY as the
coordinate system and in which all data is in arbitrary XY. For more informa-
tion, see the SDF Loader Help (SDFLOAD.HLP) located in the SDF Loader direc-
tory.
To see a complete list of the coordinate systems in Autodesk MapGuide, as
well as their corresponding codes that you use with the /COORDSYS param-
eter in the SDF Loader, refer to the file cscodes.txt that is installed with the SDF
Loader.
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118 Chapter 6 Planning and Designing Maps