In Times Square, a saxophone player plays a mournful song. His only audience is a few purposeful walkers and cyclists; the only other sounds are a public-health recording from the N.Y.P.D. and the wail of sirens. It’s unsettling to see the basketball court by the West Fourth Street subway station and the cavernous Main Concourse inside Grand Central Terminal without their normal activity and interaction. . . .Throughout the city, essential workers are still going about their work. Delivery people whiz down the streets on bikes, with backpacks full of supplies or meals. Postal carriers and shipping-company workers in masks sort through piles of boxes. Grocery-store workers keep the shelves stocked for the shoppers who queue up outside in a line that stretches down a city block, with each person standing a careful six feet from the next.