Use this dialog box to specify the source of thematic data and partition it into ranges.
Data Values area
Data Ranges area
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.
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.
When numeric data is read into the AutoCAD Map 3D 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 |