Determining the position of an electrode relative to an insulative cover

A method of determining that an instrument is exposed to a conductive medium, comprising:

• positioning the instrument within a volume;
• determining a first position of a first position element and a second position element both connected to the instrument;
• determining a second position of the first position element and the second position element connected to the instrument;
• comparing the determined first position and the determined second position;
• and
• determining whether map data collected with the instrument is valid on the basis of whether at least one of the first position element and the second position element is insulated from the conductive medium in the volume by an insulator of the instrument.