Mass appraisal model - How does a mass appraisal model value of my property?

Each property in the county has a set of characteristics that are used by the model. Some examples are its location, living area square footage, basement square footage (finished and non), style, quality, garage square footage, lot features, etc. These variables may be reviewed on sold properties used in the model in order to estimate value of the properties. The model is then applied to both sold and unsold properties.