Tijana Janjić Pfander, from the Hans Ertel Centre for Weather Research in Munich, Germany, led and published a review on the question of representation (or representativeness) error in data geophysical assimilation. She gathered and coordinated several colleagues who recently contributed to this topic. The paper carefully builds a definition for the representation error using analytical arguments. Solutions to account for the representation error are discussed. The review is illustrated with examples in meteorology, oceanography and atmospheric chemistry. Finally connections are made with recent theoretical developments in data assimilation, such as the estimation of the observation error covariance matrix. The paper will appear as a featured article in the Quarterly Journal of the Royal Meteorological Society.