All the maps we use were created especially for use on this site. Since their sole purpose is for use in educational settings, teachers are absolutely welcome to use these maps in their classrooms at any time. It is also okay to reproduce these maps, with proper attribution, for other non-commercial use.
To create the maps used on this site, we have relied on a wide range of publicly available resources. Most of the base maps we use are taken from .svg files made available in the “Blank Maps” category of Wikimedia Commons under Creative Commons licenses. In some cases, we go one step further and begin with shapefiles. Many shapefiles are available from government sites, including the United States Census Bureau. In some cases, we have found shapefile data collected on Bjørn Sandvik’s wonderful website, Thematic Mapping.
To make cartograms, we use the open-source Java application ScapeToad, which is available to download online.
Lately, we have been making a lot of dot maps and proportional symbol maps using the R language and its associated programs, which are great for statistics and free to download and use.
The statistics that go into making our maps come from many sources. We use a lot of data from the U.S. Census and American Community Survey, as well as from the various bodies of the United Nations. In a lot of cases, our maps are based on statistics cribbed from multiple sources to make our maps the best possible interpretation of confusing and conflicting data. When we post the answer for each of our maps, we cite the sources we have used and make note of any potential problems with the data or its interpretation.