Chemical analysis in a TEM has usually been done as a manual point analysis by forming a probe of an appropriate size for the area of interest. This type of local analysis may provide enough information from the selected area, but these days when materials properties are found to be deeply dependent on chemical distribution, one needs to do a higher dimensional analysis using a systematic line scan or mapping.

Since the advent of the Field Emission Gun (FEG), chemical mapping using X-rays (EDS mapping) or inelastic scattered electrons (Energy Filtering mapping) has become more and more commonly used due to the extremely high resolution information available in the chemical map. Compared to the energy filtered mapping, EDS maps take longer to acquire due to the use of the scanned probe over the area but EDS mapping allows a wider choice of elements to map due to the wider energy range it covers.