Intro to GIS Exercise #5 – Symbology and Map Layout / Design IUP ...

What is a geometric series?
A geometric series is a pattern where a constant coefficient multiplies each value in the series. For
example, a sequence of {0.1, 0.3, 0.9, 2.7, 8.1} is where each value is multiplied by 3. The inverse of 3
would be 0.33333 (or 1/3).
The table below is an example of a geometrical interval classification that was produced in ArcMap. The
interval (or bin size) of the class is calculated by subtracting the minimum from the maximum. The
geometric coefficient is calculated by dividing the previous interval by the current interval. There are two
possible geometric coefficients to create this classification structure, 1.539927 and 0.649382, which are
inverses of each other.
Geometrical Interval Classification Minimum Maximum Interval Coefficient
0.026539462 0.046593756 0.020054
0.046593757 0.059616646 0.013023 1.539927
0.059616647 0.068073471 0.008457 1.539927
0.068073472 0.081096361 0.013023 0.649382
0.081096362 0.101150655 0.020054 0.649382
0.101150656 0.132032793 0.030882 0.649382
0.132032794 0.179589017 0.047556 0.649382
Standard deviation
This classification scheme shows you how much a feature's attribute value varies from the mean. ArcMap
calculates the mean values and the standard deviations from the mean. Class breaks are then created
using these values. A two‐color ramp helps emphasize values above (shown in one color) and below
(shown in another color) the mean.
Setting a classification
About setting a classification
When you classify your data, you can either use one of the standard classification schemes that ArcMap
provides (reviewed above) or create custom classes based on class ranges you specify. If you want ArcMap
to classify the data, simply choose the classification scheme and set the number of classes.
Defining your own classes
If you want to define your own classes, you can manually add class breaks and set class ranges that are
appropriate for your data. Alternatively, you can start with one of the standard classifications and make
adjustments as needed.