Documentation

Control Bubble Size

You can use the size of the bubbles in a geographic bubble chart to communicate a quantifiable aspect of your data. For example, for Lyme disease sample data, you can use bubble size to visualize the number of cases in each county in New England. The following properties of the geographic bubble chart work together to control the size of the bubbles on the chart:

The SizeData property specifies the data that you want to plot on the chart. SizeData must be a vector of numeric data the same size as the latitude and longitude vectors, or a scalar. Another way to specify size data is to pass a table as the first argument to geobubble and specify the name of a table variable to use for size data. You use the SizeVariable property to specify this table variable. When you use a table variable to specify size data, geobubble stores the values of this variable in the SizeData property and sets the property to read-only. If you do not specify SizeData, geobubble plots the geographic locations on a map using bubbles that are all the same size.

geobubble determines the size (diameter) of each bubble by linearly scaling the SizeData values between the limits set by the BubbleWidthRange property. BubbleWidthRange is a two-element vector that specifies the smallest bubble diameter and the largest bubble diameter in points. By default, BubbleWidthRange sets the range of bubble diameters between 5 points and 20 points. You can specify a bubble diameter as small as 1 point and as large as 100 points.

Use the SizeLimits property to control the mapping between SizeData and BubbleWidthRange. By default, the SizeLimits property specifies the extremes of your data range. For example, the SizeLimits default for the Lyme disease sample data is: [0 514] when the Cases2010 variable is used as the SizeVariable.

When you specify size data, the geographic bubble chart includes a legend that describes the mapping of bubble sizes to your data. geobubble uses the values in the SizeLimits property as upper and lower bounds of the legend. When you specify a table variable, geobubble uses the variable name as the title of the size legend.

counties = readtable('counties.xlsx');

gb = geobubble(counties,'Latitude','Longitude','SizeVariable','Cases2010');
geolimits(gb,[41 47],[-75 -66])

size_data_values = gb.SizeData;
size_data_values(1:15)

ans = 15×1

   331
   187
    88
   125
   240
   340
   161
   148
    38
     4
      ⋮

size_limits = gb.SizeLimits

size_limits = 1×2

     0   514

default_width_range = gb.BubbleWidthRange

default_width_range = 1×2

     5    20

gb.BubbleWidthRange = [4 15];

Control Bubble Color

You can use the color of the bubbles in a geographic bubble chart to code them according to data category. For example, in the Lyme disease sample data, you can characterize the severity of Lyme disease in each county in New England as high, medium, or low. The following properties of the geographic bubble chart work together to control the color of the bubbles on the chart:

The ColorData property specifies the data that you want to control the color of the bubbles in your chart. ColorData must be a vector of categorical data, the same size as latitude and longitude. Another way to specify color data is to pass a table as the first argument to geobubble and specify the name of a table variable to use for color data. You use the ColorVariable property to specify this table variable. geobubble stores the values of the table variable in the ColorData property and sets the property to read-only.

If your data does not initially include a categorical variable, you can create one. For example, the Lyme disease sample data does not include a categorical variable. One way to create a variable of this type is to use the discretize function. Take the occurrences data, cases2010, and create three categories based on the number of occurrences, describing them as low, medium, or high. The following code creates a categorical variable named Severity from the occurrence data.

Severity = discretize(counties.Cases2010,[0 50 100 550],...
'categorical', {'Low', 'Medium', 'High'});

The BubbleColorList property controls the colors used for the bubbles in a geographic bubble chart. The value is an m-by-3 array where each row is an RGB color triplet. By default, geobubble uses a set of seven colors. If you have more than seven categories, the colors repeat cyclically. To change the colors used, use one of the other MATLAB^® colormap functions, such as parula or jet, or specify a custom list of colors.