Link it in to sat-nav systems and it could be very interesting. Also, to counter xirium's (perfectly reasonable) point about companies being reluctant to share

Link it in to sat-nav systems and it could be very interesting. Also, to counter xirium's (perfectly reasonable) point about companies being reluctant to share information: if you sell it to one parking company, then customers will know which of that company's car parks to go to, which is an efficiency benefit for them. If they're doing it, other companies might feel they have to as well.