You don't even need dedicated mapping programs. It's just latitudes and longitudes, so any 2D plotting program would be sufficient (as long as the data can fit into memory!).

I made this map awhile ago for Instagram photos using R/ggplot2: http://i.imgur.com/IvGox1f.png

Although the country boundaries aren't strictly necessary. Since there appears to be a demand for generating these maps, I'll work on a tutorial for this NYC data set.

Apparently, they didn't plot it on the map but on a grid. The density of data gives the well defined contour; a clever hack!