When using Print Preparation, you can define and select from a list of Scales in the "Add Rectangular Viewport" command, separate from the Plot Scales defined by a Geospatial Administrator Schema or DGNLIB file.

The scales presented in the list and those available at placement time are defined by a Workspace variable pointing to an XML file containing the appropriate scales. If this variable is not defined or the file is not found then the software provides certain built-in scales. The scale value will be calculated by NumDgnUnits / NumPaperUnits. If the unit in PaperUnitName and DgnUnitName is different, the values will be converted to the same unit first.

MS_GEOXFM_BORDER_SCALE_DOMAINLIST_FILE XML file describing the scales for the project.

The file is of the format below.
In imperial system units

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Scales name="BorderScales">
    <scale DisplayName="1&quot;=400'" name="1in=400'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="400.0" />
    <scale DisplayName="1&quot;=200'" name="1in=200'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="200.0" />
    <scale DisplayName="1&quot;=100'" name="1in=100'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="100.0" />
    <scale DisplayName="1&quot;=50'" name="1in=50'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="50.0" />
    <scale DisplayName="1&quot;=40'" name="1in=40'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="40.0" />
    <scale DisplayName="1&quot;=25'" name="1in=25'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="25.0" />
    <scale DisplayName="1&quot;=20'" name="1in=20'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="20.0" />
    <scale DisplayName="1&quot;=8'" name="1in=8'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="8.0" />
    <scale DisplayName="1&quot;=4'" name="1in=4'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="4.0" />
    <scale DisplayName="1&quot;=2'" name="1in=2'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="2.0" />
    <scale DisplayName="1&quot;=1'" name="1in=1'" PaperUnitName="Inches" NumPaperUnits="1.0" DgnUnitName="Feet" NumDgnUnits="1.0" />
</Scales>

or in metric system units:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Scales name="BorderScales">
    <scale DisplayName="1:100" name="1:100" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="100.0" />
    <scale DisplayName="1:200" name="1:200" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="200.0" />
    <scale DisplayName="1:300" name="1:300" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="300.0" />
    <scale DisplayName="1:400" name="1:400" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="400.0" />
    <scale DisplayName="1:500" name="1:500" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="500.0" />
    <scale DisplayName="1:800" name="1:800" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="800.0" />
    <scale DisplayName="1:1000" name="1:1000" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="1000.0" />
    <scale DisplayName="1:2500" name="1:2500" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="2500.0" />
    <scale DisplayName="1:5000" name="1:5000" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="5000.0" />
    <scale DisplayName="1:10000" name="1:10000" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="10000.0" />
    <scale DisplayName="1:12500" name="1:12500" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="12500.0" />
    <scale DisplayName="1:25000" name="1:25000" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="25000.0" />
    <scale DisplayName="1:40000" name="1:40000" PaperUnitName="Meters" NumPaperUnits="1.0" DgnUnitName="Meters" NumDgnUnits="40000.0" />
</Scales>

This information is available in the OpenCities Map Help documentation.