First, here is an interesting site that had a lot of information that could be used for data visualization. Each lesson is meant to show how color can be used on a map to illustrate differences between countries.
This particular site shows internet users by country:
The lesson plan, as is, is a good plan for younger students – it involves color coding countries according to the amount of Internet users. In order to be more appropriate for a high school algebra class, I would have the students derive percentages and produce other ways to show the data (e.g. pie charts, bar graphs, etc.).
It could also lead into interesting discussions as to why some countries have more users than others? Is there any scenario where the data could be misleading? Can some users be counted more than once? Could there be better way or data to understand internet usage by country?
For higher grades in high school, students could look at multiple data sets and determine if there are any correlations. For example, does GDP have any correlation to internet usage? Look at all the data sets at the www.indexmundi.com site and make a conjecture between two of the data sets. Then use a scatter plot and regression analysis to see if there is truly a correlation.