Mass Spectrometry Terminology
LC-MS map they refer to is the projection of two separation method (Liquid Chromatography - Mass Spectroscopy) results into an imaginary plane. It's a conceptual map. From this map, peptide signals referred to as "features" (article uses this term) are selected for the next level of fragmentation and then MS again.

Figure 1 of the article you cite simulates a small fraction of this larger map.