To find a data source for visualizations, I found myself commonly searching for "Top 200 Cities in the US", "largest cities by land area", and "largest meto area by population", etc.
I would then have to combine the list I found with other data sources to get all the info I needed.
I thought I'd try to keep an up-to-date copy of this list, in case others also found this helpful.
You can find that list here: https://gist.github.com/aaronhoffman/e1893d32fa1254429abf57f5c0413fa3
I will try to keep this list up-to-date with additional information and API keys as I use it over time.
Hope this helps,