Your location
Your exact location never leaves your phone.
When you share a photo or say how the haze is, the site can ask for your location to work out which area you're in. That check happens on your phone, and your coordinates are never sent or saved.
For a photo, only the area name, like North or Central, is sent. For a haze report (Clear, Hazy or Very hazy), the town you're in, like Tampines, is sent too, so others can see where it's hazy. If you say no to location, you just pick your area yourself, and no town is sent.
Haze reports show for everyone without your name, and are deleted after 3 days. To stop one person flooding them, the site keeps a scrambled code made from your IP address with each report, deleted with it.