15. A system for maintaining a calendar of a user, comprising: a processor; a calendar server executing on the processor and configured to: access an online profile of the user at a first social networking website; identify, on the online profile, a first post referencing a physical location, wherein the first post is created on the first social networking website by a client application of the user on a first calendar date, and wherein the first post comprises a timestamp of the first calendar data; identify, on the online profile, a second post referencing the physical location, wherein the second post is created on the first social networking website by a client application of the user on a second calendar date and wherein the second post comprises a timestamp of the second calendar date; calculate, and based on the timestamp of first calendar date and the timestamp of second calendar date, a first time period between user visits to the physical location; estimate, based on the first time period between user visits, a future calendar date when the user is expected to visit the physical location; create, in the calendar, an event scheduled to occur at the physical location and on the future calendar date; determine, after the future calendar date and based on the first social networking website and a second social networking website, that the user did not visit the physical location on the future calendar date; identify, on the first social networking website, a third post referencing the physical location, wherein the third post is entered by the user on a third calendar date, wherein the third post comprises a timestamp of the third calendar date, and wherein the third calendar date is after the future calendar date; calculate a modified first time period between user visits based on the third calendar date; estimate, based on the modified first time period between user visits, a new future calendar date when the user is expected to visit the physical location; and create, in the calendar, a new event corresponding to the new future calendar date.
15. A system for maintaining a calendar of a user, comprising: a processor; a calendar server executing on the processor and configured to: access an online profile of the user at a first social networking website; identify, on the online profile, a first post referencing a physical location, wherein the first post is created on the first social networking website by a client application of the user on a first calendar date, and wherein the first post comprises a timestamp of the first calendar data; identify, on the online profile, a second post referencing the physical location, wherein the second post is created on the first social networking website by a client application of the user on a second calendar date and wherein the second post comprises a timestamp of the second calendar date; calculate, and based on the timestamp of first calendar date and the timestamp of second calendar date, a first time period between user visits to the physical location; estimate, based on the first time period between user visits, a future calendar date when the user is expected to visit the physical location; create, in the calendar, an event scheduled to occur at the physical location and on the future calendar date; determine, after the future calendar date and based on the first social networking website and a second social networking website, that the user did not visit the physical location on the future calendar date; identify, on the first social networking website, a third post referencing the physical location, wherein the third post is entered by the user on a third calendar date, wherein the third post comprises a timestamp of the third calendar date, and wherein the third calendar date is after the future calendar date; calculate a modified first time period between user visits based on the third calendar date; estimate, based on the modified first time period between user visits, a new future calendar date when the user is expected to visit the physical location; and create, in the calendar, a new event corresponding to the new future calendar date. 19. The system of claim 15 , wherein identifying the first post comprises: identifying, on the first social networking website, an image uploaded by the user; and extracting, from the image, a plurality of geospatial metadata comprising a global positioning system (GPS) coordinate of the physical location.