An update to Snapchat that shows publicly posted images on a searchable map has raised safety concerns among parents.
Snap Map lets people search for places such as schools and see videos and pictures posted by children inside.
It also lets people locate their "friends" on a map that is accurate enough to determine where people live.
Snap, the company behind Snapchat, stressed to the BBC that location sharing was an opt-in feature.
Snap Map was launched on Wednesday and was promoted as a "new way to explore the world".
Video clips and photos that members have posted publicly can be discovered on the map, while members who have chosen to share their location can also be seen on the map by those they have added as "friends".
However, members can add people they have never met to their friends list too.
A message to parents posted by St Peter's Academy in Staffordshire warned that the location-sharing feature lets people "locate exactly where you are, which building you are in and exact whereabouts within the building".
One parent described the update as "dangerous" while another said she could not find the setting to disable it.
People have expressed concern online that the app could be used for stalking or working out exactly where somebody lives.
"If you zoom right in on this new Snapchat map thing it literally tells you where everyone lives? Like exact addresses - bit creepy no?" wrote one user called Leanne.
"This new Snapchat update is awful. An invitation for stalkers, kidnappers, burglars and relationship trust issues," suggested Jade.
Snap told the BBC that accurate location information was necessary to allow friends to use the service to meet, for example at a restaurant or crowded festival, and said points of interest on the map, such as schools, were provided by third-party mapping service Mapbox.
Concerned parents could find out more information on its Privacy Center website, a spokesman told the BBC.
"With Snap Map, location sharing is off by default for all users and is completely optional. Snapchatters can choose exactly who they want to share their location with, if at all, and can change that setting at any time," a Snap spokesman said.
"It's also not possible to share your location with someone who isn't already your friend on Snapchat, and the majority of interactions on Snapchat take place between close friends."
How to switch off Snap Map location sharing
- When in photo-taking mode, pinch the screen to open Snap Map
- Touch the settings cog in the top right corner of the screen
- Tap "Ghost Mode" to switch off location sharing
- Photos and videos posted to Snapchat's public 'Our Story' will still be discoverable on the map