For now, Snapchat is starting with 10 major cities: New York, San Francisco, Los Angeles, Honolulu, London, Paris, Sydney, São Paulo, Riyadh, and Washington, DC. Just like normal stickers, geostickers can be sent in chat messages, stuck anywhere on top of snaps, or be pinned inside of videos.
It seems like a good feature:
Geostickers are a small but neat addition to Snapchat's photo editing arsenal that should help to make messages feel a bit more personal, since they're exclusive to where a person's actually standing. It's easy to imagine that, like geofilters, these could get opened up in the future to let more cities and locations offer new ways to customize your snaps.
Meanwhile, Instagram just cloned Snapchat inside its own app, minus all the cool stuff like stickers and lenses.