One of the most important tasks an appraiser performs is to assimilate data. Data can be split into Specific or General. Specific data is from the home itself; Location, condition, amenities, size and other specific data are documented by the appraiser during an inspection.
General data is gathered from a many sources. Local Multiple Listing Services (MLS) provide information on recently sold homes that might be used as comparables. Tax records and other public documents verify actual sales prices in a market. Appraisers often need to report when a property lies in a flood zone, and that information is retrieved from a FEMA data outlet such as a la mode's InterFlood product.
And last but not least, the appraiser assimilates general data from his or her past experience in creating appraisals for other houses in the same market.