a channel map in an electronic television program guide system that includes channel numbers and alphanumeric channel labels is updated . the tuner in the system is tuned to a channel number of a television channel that is included in the channel map . data is extracted from the television signal that includes an alphanumeric label for the tuned television channel . the channel mapis revised according to the alphanumeric label for the tuned television channel if the alphanumeric label in the extracted data for the tuned television channel does not correspond with the alphanumeric channel label stored in the channel map for the tuned television channel .