Using SharePoint’s List or Library mode means being limited
to obtaining data from a list or a library within the same
site, or in a different site on the same site collection, to create a
chart. However, the data you require is likely to be saved across many
different sites. To collect data from various sources, you can use Bamboo’s
List Rollup Web Part.  Here I’ll present
a step-by-step guide of how the process works.

This is default settings of Bamboo List Rollup mode.

We have two Aggregation Services to
select: List Rollup Schema and List Rollup Data View.

For List Rollup Schema, you can enter a site URL with Absolute
Path or Relative Path, then click the Connect button to load the created
schema.

For List Rollup Data View, enter only the Site URL with Absolute Path, then click Connect to load the created schema. 

Here is an example using the LRU Schema to create a chart.

Select the field for Category and Series.

Customize the X-Axis and the Y-Axis.

And display the chart as you require it.