Aiming at solving the colour union, variation and loss problems during cross-media reproduction in the layer-tinted map, this study proposes a colour gamut mapping model for the preservation of visual differentials in layer-tinted maps. First, many layer-tinted maps are collected for analysis and the colouring rules are concluded. Then, the dominant and non-dominant colours are extracted based on the colour gamut characteristics of the maps. For the mapping of dominant colours, the corresponding Munsell's three colour dimensions are calculated by establishing the transformational relation between CIELAB colour space and Munsell's colour system and then the colour gamut mapping of dominant colours is achieved in the Munsell's colour order system. On the other hand, the mapping of non-dominant colours is achieved by hue-angle preserving minimum ΔE clipping. The experimental results indicate that compared with the four colour gamut mapping methods recommended by the International Color Consortium, the proposed algorithm in this study can more easily distinguish the hierarchical information in the maps and perfectly remain the visual differentials among the layered colours.