C/o
unofischalFurthest North: London, England, UK. 51°30′N 0°8′W
Furthest South: San Antonio, TX, USA. 29°26'N 98°30'W
Furthest East: Paris, France. 48°52′N 2°20′E
Furthest West: San Francisco, California, USA. 37°46'N 122°26'W
Highest Elevation: Sunspot, New Mexico, USA. 2,788 m (9,147 ft)
Lowest Elevation: New York City, NY, USA. 1m (3ft)
Surprisingly, Nogales, Sonora, Mexico isn't the furthest South (31°20'N, 111°00'W), and Halifax, Nova Scotia, Canada isn't the furthest North (44°39′ N 63°35′ W), though I guess I should've known that one. Paris barely beats out Nancay (47º23'N 2º12'E) for furthest East. I googled a bit for altitudes of NYC and Boston, and supposedly NY is slightly lower (I guess on average?) than Boston. Maybe if I've been in various basements in NYC that'd be even lower. :-P Greenwich, suburb of London, which I've been to, is located at 51°28'38"N 0º0'0"EW (by definition).
ETA:
A few of us are tied with a lowest elevation of "sea level" plus or minus a few meters. I propose that duration of time at that elevation be the tie breaker.
Lowest Elevation: New York City, NY, USA, 1m (3ft). 18 years 6.5 months (January 26 1978 - mid August 1996).