In advance of Facebook's possible location announcement tomorrow, Foursquare is tweaking its privacy settings today. In an announcement made on the company's blog, Foursquare says that its service will now allow you to change your settings to withhold or share more information with your Foursquare friends. For example, Foursquare is now allowing users to choose to share your email or phone number with friends or choose to opt out of all Mayorships. You can choose whether local merchants can see when you’ve checked into their businesses, and can regulate the syndication of your check-ins and activity to Twitter and Facebook. A Privacy 101 page gives you details on type of information that can be shared on the location-based network. The startup has even created an elaborate grid that breaks down how certain default settings effect the information that is shared with your friends and the public. The startup even goes so far as to provide definitions of what a check-in is and the difference between a mobile app and the website.