1. A method for tracking an activity of a user, the method comprising: downloading, over a network, web page content that comprises a tracking code; tracking, at least partially by executing the tracking code by a user computer, user activities that are responsive to at least a portion of the downloaded web page content; associating each user activity with properties of the user activity; generating user activity information consisting of each tracked activity and its associated properties, wherein the properties of the user activity are associated with a position and size of each element of a portion of a web page related to the user activity, thereby providing the user activity information an invariant form in which the user activity information is relative to the position and size of the each associated elements of the portion of the web pace; wherein the user activity information in the invariant form further allow for a compensation of differences between visual representations, wherein the compensation comprises converting, in a non-linear transformation, information within the user activity information representative of the position and size of the each associated element of the portion of the web pace to a different position and a different size for a playback display, wherein the non-linear transformation comprises converting the each associated element of the portion of the web page in a piece-wise-linear fashion; compressing and buffering a portion of the user activity information; and transmitting to a tracking entity, at least a compressed portion of the user activity information when a first transmission criterion is fulfilled.