Today's data (both geoJSON and CSV) for the first SVG come from the DataSF municipal open data initiative. I used mapShaper to convert the geoJSON file into a topoJSON file (which is much smaller for reasons discussed during the first geo coding lecture).
The second SVG will make use of a fast food dataset from Kaggle.
For contour mapping (whether using geography or not), it's better to keep the TopoJSON import around. More on d3.contour. Here is a contour example and a density example.
Contour map: