The Data Commons Knowledge Graph (DCKG) is constructed by synthesizing a single Knowledge Graph from many different data sources. It currently contains data from Wikipedia, the US Census, NOAA, FBI, etc. The browser can be used both to explore what data is available and to understand the graph structure, to help use the API.
At this point, most of the data in DCKG is about places --- cities, counties, states. You can use the search box above or start looking around from some well known starting points: