Consider looking at the Comparison of Charting modules. Here is a quote from it:
There are a variety of modules that facilitate the creation of charts. When it comes to charting in Drupal, the saying "There's a module for it" doesn't really apply. In this case, it's more accurate to say, "There are plenty of modules for it" ...
These modules support for various charting libraries that may be desirable based on a site's desired appearance, feature-set, and licensing needs.
Using the Charts module is one of the options to consider. Here is part of what's currently included in that link (its project page):
Transform Data into Information. Charts are a very good way to visualize a lot of data in a way that can be quickly digested.
Wide chart type support: Pie, Line, Bar, Column, Area or Scatter charts.
API: A Drupal-friendly syntax for creating charts easily, regardless of the underlying library.
Views integration: Display the Views results as charts.
Examples: The module includes lots of example charts for you to reference when building your own charts or chart library integration.
Supported charting libraries: out of the box, you may use either (the new) Google Charts (GC for short) or Highcharts (HC for short) as the charting library.
For 'documentation' about the charts module, you may want to start from its community documentation.
There is an issue also that might be worth looking at, about Graph node input over time (support date formatting on a continuous axis). In Comment #3 of that issue is stated: 'The trouble here is that neither Views nor Date modules provide aggregation options for date-based fields'.
Disclosure: I'm the author of the comparison (+ co-maintainer of the charts module), I hope this does not violate the site's policy on self-promotion.