Linking Attribute Data To Another Database; Preparing Attribute Data For Themes - Autodesk 15606-011408-9320 - MAPGUIDE R6.3 CPU MODEL-UPG 4/5 MIN 2 CPUS INITL User Manual

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troubleshooting
problems creating themes
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94 Chapter 5 Working with Data in Autodesk MapGuide
a secondary OLE DB database table containing the name and linked URL for
each lake, and another OLE DB database table containing theme informa-
tion, such as the size of each lake, water purity, and more. When you create
the layer in the Map Layer Properties dialog box in Autodesk MapGuide
Author, you would specify the secondary table on the Data Sources tab, and
specify the theme table from the Styles tab when adding a theme. Note that
neither of the tables need to contain coordinates—they are linked to the
polygons in the SDF only by their keys. For more information, see "Creating
Themes" on page 163.
To avoid potential conversion problems, be careful when creating the key
field. Depending on the type of database, you might not be able to use the
attribute data unless the key field in the database is exactly the same size as
the key field in the SDF to which you are linking it. Some databases, when
queried, will append the keys with blank space characters to make them the
exact length you specified for the field, so the database keys will not match
those in the SDF. For more information, choose Help
Index tab, and look up "troubleshooting, problems creating themes."

Linking Attribute Data to Another Database

You can create point layers and text layers from OLE DB data sources instead
of SDFs. For these layers, you can still use an OLE DB database table for
creating themes. For example, if you are setting up a layer of cities, you might
have two tables: one that contains basic information about each city, such as
the key, coordinates, name, and a URL link, and a second table that contains
data on which you want to create themes, such as the population, majority
political party, and so on. The second table would also contain the same key
values as the first table; Autodesk MapGuide uses these keys to assign the
theme values in the second table to the corresponding cities in the first table.

Preparing Attribute Data for Themes

As mentioned in the previous sections, you can use the data in a linked
attribute table as the basis for themes. Themes draw the map features on a
layer according to particular values. For example, on a map layer that
contains cities, you could use different symbols to represent cities that fall
within different population ranges. Themes also help to differentiate features
in a layer. For example, on a roads layer, you could draw interstate highways
differently from city streets, even though they're on the same layer.

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