This repo produces a line chart and a table of populations within various distances of city centers for 200 somewhat randomly selected large cities. Data comes from https://sedac.ciesin.columbia.edu/data/collection/gpw-v4.

You can edit the HTML or JS to change some style, but there is not too much else to easily modify.

Read the blog post answering some population questions at https://triplelog.com/blog/what-is-the-population-of-that-region.html