We stopped by the offices of the Downtown Brooklyn Partnership at 15 Metrotech Center last week. It turns out to be the perfect perch for keeping an eye on the Flatbush Extension building boom. Pictured here, clockwise from top right: 1) 180 Myrtle, supermarket kingpin and aspiring politican John Catsimatidis’ 500-unit mixed-use development; 2) 156 Myrtle, BFC’s 37-story condo project currently in high gear; 3) 157 Myrtle, the half-block of low-rise properties awaiting the wrecking ball courtesy of rentals-only developer AvalonBay. Kinda puts it all in perspective, huh. GMAP