Ground-based vector and total-field scalar magnetometer time series are a cornerstone of the USGS' geomagnetic data services and research. These data include: near real time uncorrected magnetic "variation" data, taken from sensors roughly aligned with the local magnetic meridian; near real time "adjusted" data, which are corrected to align with geographic coordinates; archival "quasi-definitive" and "definitive" data, which have been further calibrated and cleaned to satisfy INTERMAGNET data quality standards; and various derived data products and indices used to assess and mitigate space weather and geomagnetic hazards. The "Plots" web application is an intuitive and flexible online visualization tool that allows users to select different geomagnetic data products, compare magnetic observatories and data channels, zoom into and pan across time intervals of interest, and retrieve the digital data used to generate the time series plots easily via a modern application programming interface (API).