The NDVI map is a mosaic of multiple images. Depending on the weather, each image may have been taken at a different date. WEB: The date displayed at the bottom of the screen is the one of the image pointed by your mouse. MOBILE: The date displayed at the bottom of the screen is the one of the image at the center of your map view. iPAD: Click on the map to display the date in a tooltip at the bottom of the map.