A volume of a patient can be mapped with a system operable to identify a
plurality of locations and save a plurality of locations of a mapping
instrument. The mapping instrument can include one or more electrodes
that can sense a voltage that can be correlated to a three dimensional
location of the electrode at the time of the sensing or measurement.
Therefore, a map of a volume can be determined based upon the sensing of
the plurality of points without the use of other imaging devices. An
implantable medical device can then be navigated relative to the mapping
data.