A method performed by a digital map enhancement system for improving accuracy of pre-stored digital map data of a digital map adapted to be utilized by a vehicle, said method comprising: determining a current position of said vehicle; identifying, in said pre-stored digital map data, a mapped digital landmark representing a stationary landmark predicted to be in the vicinity of said current position of the vehicle, said mapped digital landmark comprising a pre-stored position of said stationary landmark; detecting said stationary landmark by means of one or more sensor devices on-board the vehicle, said one or more sensor devices being adapted for observing the surroundings of said vehicle; determining a detected position of said stationary landmark based on said current position of the vehicle and said detecting; said method being characterized in further comprising: determining an accuracy confidence level of said detected position based on: a magnitude of a distance between said determined current position of the vehicle and said detected position of the stationary landmark; and/or type and/or types of said one or more sensor devices; and/or a number of the one or more sensor devices; comparing the determined accuracy confidence level of said detected position with a predetermined accuracy threshold and with an accuracy confidence level value of the pre-stored position; and updating, if said determined accuracy confidence level of said detected position is greater than said predetermined accuracy threshold and greater than the accuracy confidence level value of the pre-stored position, said pre-stored position comprised in the mapped digital landmark, with said detected position of the stationary landmark. determining a current position of said vehicle; identifying, in said pre-stored digital map data, a mapped digital landmark representing a stationary landmark predicted to be in the vicinity of said current position of the vehicle, said mapped digital landmark comprising a pre-stored position of said stationary landmark; detecting said stationary landmark by means of one or more sensor devices on-board the vehicle, said one or more sensor devices being adapted for observing the surroundings of said vehicle; determining a detected position of said stationary landmark based on said current position of the vehicle and said detecting; determining an accuracy confidence level of said detected position based on: a magnitude of a distance between said determined current position of the vehicle and said detected position of the stationary landmark; and/or type and/or types of said one or more sensor devices; and/or a number of the one or more sensor devices; comparing the determined accuracy confidence level of said detected position with a predetermined accuracy threshold and with an accuracy confidence level value of the pre-stored position; and updating, if said determined accuracy confidence level of said detected position is greater than said predetermined accuracy threshold and greater than the accuracy confidence level value of the pre-stored position, said pre-stored position comprised in the mapped digital landmark, with said detected position of the stationary landmark. a magnitude of a distance between said determined current position of the vehicle and said detected position of the stationary landmark; and/or type and/or types of said one or more sensor devices; and/or a number of the one or more sensor devices; comparing the determined accuracy confidence level of said detected position with a predetermined accuracy threshold and with an accuracy confidence level value of the pre-stored position; and updating, if said determined accuracy confidence level of said detected position is greater than said predetermined accuracy threshold and greater than the accuracy confidence level value of the pre-stored position, said pre-stored position comprised in the mapped digital landmark, with said detected position of the stationary landmark.