  Understanding human mobility dynamics among places provides fundamental
knowledge regarding their interactive gravity, benefiting a wide range of
applications in need of prior knowledge in human spatial interactions. The
ongoing COVID-19 pandemic uniquely highlights the need for monitoring and
measuring fine-scale human spatial interactions. In response to the soaring
needs of human mobility data under the pandemic, we developed an interactive
geospatial web portal by extracting worldwide daily population flows from
billions of geotagged tweets and United States (U.S.) population flows from
SafeGraph mobility data. The web portal is named ODT (Origin-Destination-Time)
Flow Explorer. At the core of the explorer is an ODT data cube coupled with a
big data computing cluster to efficiently manage, query, and aggregate billions
of OD flows at different spatial and temporal scales. Although the explorer is
still in its early developing stage, the rapidly generated mobility flow data
can benefit a wide range of domains that need timely access to the fine-grained
human mobility records. The ODT Flow Explorer can be accessed via
http://gis.cas.sc.edu/GeoAnalytics/od.html.
