Gregory's Server@Edent Most of it is a data quality problem in deciding on the predicate to filter the data.
Do you wanna check into an untitled tree or water fountain in your local park? (Filter things without a name?)
What about checking into a whole city or country? Or a particular borough? Or an area that doesn't line up with a governmental/administrative area (Soho, say)? That's a thing people did on 4sq to tell friends they are visiting.
How about the M25? (This place is not a place of honour etc.)
@tommorris @Edent also answers aren’t necessarily consistent; you might not have enough data to filter it in the way people want. people might want to check in to Route 66, but not the M25.