Create a bubble chart and add a bubble legend.

x = 1:10;
y = exp(-0.5*x) +  .05 * randn(1,10);
sz = randi([20 500],[1,10]);
bubblechart(x,y,sz)
bubblelegend('Population')

Create a bubble chart and add a bubble legend. Specify the 'telescopic' style for a more compact presentation.

x = 1:15;
y = exp(-0.5*x) +  .1 * randn(1,15);
sz = randi([20 500],[1,15]);
bubblechart(x,y,sz)
bubblelegend('Population','Style','telescopic');

Create a bubble chart. Then call the bubblelegend function with a return argument to store the BubbleLegend object as blgd. Move the legend outside the plot box by setting the Location property on the object to 'northeastoutside'. Display two bubbles instead of three by setting the NumBubbles property to 2.

x = 1:50;
y = rand(1,50);
sz = randi([20 500],[1,50]);
bubblechart(x,y,sz)

% Create bubble legend and set properties
blgd = bubblelegend('Population');
blgd.Location = 'northeastoutside';
blgd.NumBubbles = 2;

When you display multiple data sets with different colors or different types of plot objects, you can include multiple legends. To manage the alignment of the legends, create your chart in a tiled chart layout.

Create two sets of data, and plot them together in the same axes object within a tiled chart layout.

x = 1:20;
y1 = rand(1,20);
y2 = rand(1,20);
sz1 = randi([20 500],[1,20]);
sz2 = randi([20 500],[1,20]);

% Plot data in a tiled chart layout
t = tiledlayout(1,1);
nexttile
bubblechart(x,y1,sz1)
hold on
bubblechart(x,y2,sz1)
hold off

Add a bubble legend for illustrating the bubble sizes, and add another legend for illustrating the colors. Call the bubblelegend and legend functions using a return argument to store the legend objects. Move the legends to the east tile by setting the Layout.Tile property on each object to 'east'. Placing the legends together in a tile keeps them aligned.

blgd = bubblelegend('Population');
lgd = legend('Springfield','Fairview');
blgd.Layout.Tile = 'east';
lgd.Layout.Tile = 'east';