Facebook Places is Facebook's geolocation feature. When it w as deployed, all Facebook users were automatically set to publicly reveal their location.
Not only that, but friends are able to tag users as being at a certain location, meaning even users not intending to tag themselves could suddenly find their location is public on Facebook.
Go to Account > Privacy Settings, then change your setting for "Places I check in to"
to whatever you're comfortable with.
Then uncheck the option to "Include me in 'People here now' after I check in".
"Facebook Tips: Controlling “Places”"