[Mg/Fe] vs. [Fe/H] plane for the HARPS sample with reliable age estimates. The blue line denotes our chemical separation between thin and thick disks, where the thick disk stars (star symbol) are shown above the line and thin disk stars (circle symbol) below the line. The size of each data point denotes the relative age of each star; the larger points are older than smaller points. Stars are color coded by their R_p. The color bar stops at R_p = 7 kpc to prevent color saturation of stars coming from the inner Galaxy. Which sequence the most metal-rich, solar-[Mg/Fe] stars belong to is unclear, and we show the red line as an example of a different potential split between stellar population groups.