Use this dialog box to specify the source of thematic data and partition it into ranges.
Data Values area
- Obtain From
-
Click
. In the Choose Data Expression dialog box, select the data source from the lists under Properties, Link Templates, Blocks, or Object Data. - Ignore
-
Select data values to exclude from the thematic display. These values, while present in the data, may be inappropriate for use in the thematic map. Examples include null or empty data values.
- Normalize By
-
Enter a value or an expression if you want to normalize the data values relative to some other data value. Click
to display the Choose Data Expression dialog box. - Read Data
-
Reads the data from the data source according to the expression you defined.
Data Ranges area
- Group Value By
-
Select a method for partitioning data values.
Optimal The optimal method groups data values based upon a determination of the natural breaks in the data. Because the calculations are iterative, this method quite literally finds the optimal sets of values in a group based upon the position of values upon a number line. It is most useful for complex non-uniform distributions where calculation time is less important than the accuracy of grouping. This is the default method.
Quantile Divides the data so that each range contains an equal number of values. Also known as equal count, this method is most appropriate where the data values are linear (equally distributed).
Equal Interval Divides the data into a specified number of groups from the minimum value to the maximum. Also known as equal step, this method has the disadvantage that it may over generalize the data and place too many values in one range and too few in another.
Standard Deviation This method calculates how far data values differ from the arithmetic mean. It is most effective when the data approximates a normal distribution (bell-shaped curve). This is rarely the case with geographical data, but is fairly common when considering demographic data. Because of this curve preference, standard deviations are best used with an even number of groups. Standard deviations are often used to emphasize how far a specific value is above or below the mean value.
- Number
-
Select the number of ranges to create.
- Precision
-
Specify the numeric precision. This option rounds the values up or down to the decimal point you specify. Rounding only affects the range value calculations and resulting range divisions. It does not affect the actual data values stored in the data source. For more information, see Notes About Precision below.
- Use Thousands Separator
-
Adds a punctuation mark to separate the thousands in values such as population data.
- Find Ranges
-
Divides the data into ranges according to the parameters you entered.
- Ranges Area
-
This area displays the data divided into ranges according to the parameters you entered.
Notes About Precision
When numeric data is read into the AutoCAD Map 3D toolset as part of thematic mapping, it is stored as an eight byte floating point number. You may fine-tune the formatting of these numbers by selecting a decimal precision or integer rounding up.
For instance, suppose you have a number that was originally entered into a database or into an object data field with the value 12.34. This number could be displayed in several ways depending upon the format specified. Formats that contain a decimal point will generate the specified number of digits to the right of the decimal point. Formats without a decimal point will round up. The following table will make this more clear.
| Format | Explanation | Ouput |
|---|---|---|
| .01 | use two decimal points | 12.34 |
| .1 | use one decimal point | 12.4 |
| 1 | nearest whole number | 13 |
| 10 | nearest ten | 20 |
| 100 | nearest hundred | 100 |