Autodesk 15606-011408-9330 User Guide - Page 99

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. When setting up your attribute data, you should consider whether you will be creating themes, and whether the data in the table lends itself easily to this task. For example, for a roads layer, do you already have a column that contains the text "Interstate" or "City Street" for each feature in the table? If so, it will be very simple to specify this column as the theme column and specify that if the column contains "Interstate," the feature will be drawn as a thick yellow line, and if the column contains "City Street," the features will be drawn as a thin black line. However, if you want your roads to be drawn in such a way as to show how heavy the traffic is, a column indicating whether it's an interstate highway or city street will not be useful-you will need a column that indicates how much traffic each road has. You can then use this third column to specify how the roads are drawn to show traffic. For example, you might create four theme categories: fewer than 200 cars per month, between 201 and 5,000, between 5,001 and 10,000, and greater than 10,000. You can then specify the display attributes separately for each of these categories, so that roads with the lightest traffic are drawn in thin black lines and roads with heaviest traffic are drawn in thick red lines, and so on. If you are using point or text data, you need to consider which symbols you will want to use for each theme category. For more information, see "Working with Symbols" on page 109. Setting Up Your Attribute Database You need to take the following points into consideration when setting up your attribute database:
Before Autodesk MapGuide can use your databases, you must set them up and configure them as OLE DB data sources or Autodesk DWG data sources. For more information, see "Setting Up Your Data Sources" on page 78.
You can limit users' access to data sources by setting up passwords for users or for groups or by assigning access keys to the resource. For more information, see "Managing Server Security" on page 80. Working with Attribute Data | 99