Here is a relatively easy way to create a quick thematic map, based on Object Data. In addition to Object Data, this tutorial also requires some familiarity with the Task Pane and using Queries to bring Source Drawings into Current Drawings. These and other basic Map 3D topics are covered in detail in our book “Digging Into AutoCAD Map 3D 2011”.
Our book shows you how to alter the properties of AutoCAD objects when querying them into a current drawing, based on object data values. This tutorial takes it a step further, altering properties different ways, based on ranges of data. In this example, we start with a drawing of line segments representing streets. These were imported from a GIS Shapefile, and an object data table was created to contain the data, which includes the speed limit of each street segment. From this, a simple thematic map will be created, with color-coded streets based on where these speed limits fall within two ranges: those 35 MPH and under, and those over 35 MPH.
To begin, start with a new blank drawing, and attach the Streets drawing to it, using the Map Explorer tab of the Task Pane. Next, define a new query. There will be multiple elements to this new query, a Location element and an Alter Properties element.
For the Location element, simply include All (to get all of the geometry in the Streets drawing).
To set up the other element, click the Alter Properties button.
Select Color as the property to alter. This activates the Expression section. Click the Ranges… button to set up a Range Table.
Create a new Range Table called Speed, and give it a description, then add two ranges to the table. From the Operator drop-down list, select“<=” (less than or equal to). For the Expression value enter 35, and for Return Value enter 1. This will assign the AutoCAD color #1 (red) to all streets with a Speed value of 35 or less. Click the Add button (very important!) to add this expression to the Current Range Table Definition.
Next, create another expression to assign the color 3 (green) to all streets with a speed value greater than 35. Click the Add button again to add this second expression to the table. Click the OK button to add save the Range Table called Speed, and return to the Alter Propertiesdialog box.
Click the Expression button, and then select the Object Data field Speed. Click OK to dismiss the Property Alteration Expression dialog box and return to the Alter Properties dialog box.
Select the new Range Table you just created, called Speed, from the Range: drop-down list, then click the Add button, to add the complete expression to the Current Property Alterations list at the top of the dialog box. Click the OK button to return to the Define Query of Attached Drawing(s) dialog box.
Select the Query Mode Draw, then click the Execute Query button.
Notice that when the Streets drawing is queried into the Current (blank) drawing, all of the local streets (35 MPH and under) are colored red and the arterials and highways (above 35 MPH) are colored green.
This is one quick way to make a type of thematic map, by altering properties based on ranges of values. It is particularly appropriate if you are performing a query anyway, or if you are sharing your finished drawing with users who do not have Map 3D. With this technique, the actual AutoCAD properties have been altered, as opposed to the temporary display changes that occur when you are using the Display Manager in Map to create a Thematic Map.
Alter property queries can also be used to change many other AutoCAD object properties, including layer, linetype, lineweight, rotation and scale.
If you would like to have a copy of the dataset used in this tutorial, and a list of more detailed steps, use the Contact Us form and selectGeneral Feedback to request it from Russell Martin.
