That depends very much on your definition of "London" and "Denver". Your first figure refers to the population density of Greater London, a vast area covering m

That depends very much on your definition of "London" and "Denver". Your first figure refers to the population density of Greater London, a vast area covering much of what used to be the Home Counties. Your second figure refers solely to Denver City rather than the broader Denver-Aurora-Lakewood metropolitan statistical area, much of which is functionally suburban Denver. I don't think it's particularly useful to attempt to pin down a fixed definition of the boundaries of either city, particularly one as amorphous as London. Suffice it to say that London is densely populated, Inner London is even more densely populated and rush hour on the tube is genuinely insane; Londoners regularly encounter densities that simply don't occur in most US cities outside of a football stadium and have a subsequent need for far higher throughput than 4G can deliver.