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Chapter 6 Planning and Designing Maps
layers should fall within which of these three display ranges and set display
ranges for them accordingly. For more information, see “Creating a Design
Spreadsheet” on page 114.
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 coordinate preci-
sion you want, and how to set up and use a design spreadsheet—as well as
following general design guidelines.
About Coordinate Systems
A coordinate system is a description of the origin of your map, the projection
system used, and the units you are using; it describes how the sphere of the
earth is projected onto a sheet of paper and converted to the Cartesian coor-
dinate system.
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 coordinate 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 coordinate pair corresponds to one exact point on
the earth.
Some types of arbitrary xy coordinate systems, such as the state plane coor-
dinate systems, make use of both of these concepts. Each coordinate system
represents 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 repre-
sents 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.