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androidplot/docs/bubblechart.md

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+# Bubble Charts
+A `BubbleChart` is a two dimensional representation of three dimensional data
+on an `XYPlot`, where the xy values are drawn as a circle with a radius representing the zVal.
+
+![image](images/screens/bubble_horiz.png)
+
+# Basic Usage
+The first step in creating a `BubbleChart` is to define the data to be plotted.  We'll start
+by creating an instance of `BubbleSeries`:
+
+Using the implicit iVal for x:
+
+```java
+BubbleSeries series1 = new BubbleSeries(
+    Arrays.asList(new Number[]{3, 5, 2, 3, 6}),        // xCoordinate
+    Arrays.asList(new Number[]{1, 5, 2, 2, 3}), "s1"); // yCoordinate
+```
+
+Or it's equivalent four argument counterpart:
+
+```java
+BubbleSeries bubbleSeries = new BubbleSeries(
+    Arrays.asList(new Number[]{0, 1, 2, 3, 4}),        // xCoordinate
+    Arrays.asList(new Number[]{3, 5, 2, 3, 6}),        // yCoordinate
+    Arrays.asList(new Number[]{1, 5, 2, 2, 3}),        // zVal (corresponds to radius) 
+    "s1");
+```
+
+Next, create a `Formatter` defining the fill and outline colors of the bubbles:
+
+
+```java
+// draw bubbles with a green fill and white outline:
+BubbleFormatter formatter = new BubbleFormatter(Color.GREEN, Color.WHITE)
+```
+
+Finally, add the `BubbleSeries` to our plot as you would any other `XYSeries` instance:
+
+```java
+plot.addSeries(bubbleSeries, formatter);
+```
+
+# BubbleScaleMode
+By default, `BubbleRenderer` scales each rendered bubble radius using the square root  of it's corresponding
+zVal, preventing apparent size differences in each bubble radius from being visually misleading.  See: https://en.wikipedia.org/wiki/Bubble_chart#Choosing_bubble_sizes_correctly
+
+If you'd prefer to use a linear scale:
+
+```java
+plot.getRenderer(BubbleRenderer.class).setBubbleScaleMode(BubbleRenderer.BubbleScaleMode.LINEAR);
+```
+# Example
+Check out the [bubble chart example source](../demoapp/src/main/java/com/androidplot/demos/BubbleChartActivity.java) for a full source example of a bubble chart.