Halfway between Greenpoint and Harlem
The midpoint on a map is rarely the fair place to meet. Greenpoint — only the G, which changes everything. Harlem — express trains make it closer than it looks. Which means the spot where you both travel for the same length of time sits somewhere other than the middle of the line between you.
Working out the fair zone by transit… this takes a few seconds, because the routing service allows one request per second.
Why travel time, not distance
If one of you drives and the other takes transit, a geographic midpoint hands one person a twenty-minute trip and the other an hour. AMICHEMIN computes the area each person can reach in a given time, then finds where those areas overlap — and inside that overlap, the point where everyone’s journey is closest to equal.