On template day, you may still need to make some decisions. Decide how much of the sink will show on an undermount install. If keeping the sink clean with little hassle is a priority, have the contractor bring the edge of the countertop flush with the walls of the sink. If you prefer the look shown here, where some of the top flange shows all around, let your installer know. Ask where the seams will be. Very few counters lack seams. In stone with veining, you may be able to hide a seam along a vein, and colored epoxies should make all seams hard to spot.