Download the app, pop in your ear buds, and start charting your personal path through the 840 acres of Central Park, with musicians of the New York Philharmonic for virtual company. As you perambulate, you’ll drift in and out of musical “cells” designed by the Pulitzer Prize-winner Ellen Reid to harmonize with the changing landscapes. Another site-specific installation of Reid’s is active now at the Saratoga Performing Arts Center upstate in Saratoga Springs, with more to follow in Philadelphia; Vienna, VA; and Jacksonville, OR. —M.G.