Autodesk 15606-011408-9320 User Guide - Page 94

a secondary OLE DB database table containing the name and linked URL for each lake, and another OLE DB database table containing theme information, 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. Online Help Index To avoid potential conversion problems, be careful when creating the key troubleshooting field. Depending on the type of database, you might not be able to use the problems creating themes 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 Contents, click the 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. 94 | Chapter 5 Working with Data in Autodesk MapGuide