A 50-state survey is a specialized secondary source that compares laws on a particular topic across all 50 states. They might be as lengthy as a book treatment or as slim as a list of states with simple citations to relevant cases, statutes, or regulations.
Lexis and Westlaw offer 50 state statutory and regulatory surveys. You can find them on both services by clicking on the Content [types]-->Statutes link on the home page and then looking in the Resources box on the right side of the screen. Alternatively, start typing 50 state survey… and select the suggested source from the dropdown list. Be sure to note the date of the survey and update your research.