Since geographic boundaries change over time, data from earlier census releases might not be available in current boundaries. Selecting a historical census geographic year allows you to access data and locations that are in older census geographic units by filtering the data and locations available in the tabs on the left side of the screen.
For example, if you select the 2000 census geographic year you will only see locations from 2000 and data that is compatible with the 2000 geographic year, all other data and locations will be hidden. You can then search for and add these data variables and locations to your project.
To Access Historical Data:
To activate Historical Mode, click on Project Settings and toggle On the Historical Views option:
With Historical Views now activated, you may create a new view with historical boundaries by selecting New View and toggling the available check box:
Click on the Year you see to toggle between historical boundaries:
When you have chosen a year, feel free to create any view that you see available, and your year options available for data variables will be present based on your chosen geographic year. For example,
Census Geographic Year 2000 will have data for: 2000, 2003, 2007 to 2012
Census Geographic Year 1990 will have data for: 1990, 1992 to 1999
Census Geographic Year 1980 will have data for: 1980 to 1989
Note: You may not have all of the options in the image above as some of the historical geographic years are for specialized datasets that your institution may not subscribe to.
See the image below - notice the years available are present based on switching to 2000 geographic boundaries: