R Packages
OpenStreetMapRgoogleMapsGGMapMaps
Heatmap
Source:http://www.businessinsider.com/i-quant-ny-manhattan-subway-map-farthest-apartment-2014-10
OSM Tiles
Source: http://blog.fellstat.com/?p=356
OSM - Nodes & Ways
Source: http://journal.r-project.org/archive/2013-1/eugster-schlesinger.pdf
OSM Polygons
Source: http://journal.r-project.org/archive/2013-1/eugster-schlesinger.pdf
OSM Navigation
Source: http://journal.r-project.org/archive/2013-1/eugster-schlesinger.pdf
To Conclude...
Visualizing Maps is more interesting than you think.