1. A method of predicting parking availability for a geographic area, comprising: defining a Markov Random Field (MRF) model for estimating a number of mobile devices used within the geographic area; applying current data describing a number of mobile devices currently observed within the geographic area and historical data describing a number of mobile devices historically observed within the geographic area to the MRF model to produce an estimate of a number of mobile devices currently being used within the geographic area; predicting a geographic population density for the geographic area responsive to the estimated number of mobile devices currently being used within the geographic area; applying the predicted geographic population density to a parking availability model to produce a prediction of the parking availability for the geographic area, wherein the parking availability model comprises a function relating predicted geographic population density for the geographic area to predicted parking availability for the geographic area; and storing the predicted parking availability for the geographic area in a computer-readable storage medium.