What is it
From the Bigquery Geo Viz site:
BigQuery Geo Viz is a web tool for visualization of geospatial data in BigQuery using Google Maps APIs. You can run a SQL query and display the results on an interactive map. Flexible styling features allow you to analyze and explore your data.
When to use it
When you need to plot geospatial data on a map. It should be used mainly for ad-hoc analysis or debugging of a limited output from a BigQuery SQL query.