Cartographic generalization or map generalization is the process of graphically reducing information from reality or larger scaled maps to display only the information that is necessary at a specific scale.
A map is always a smaller scaled representation of reality, thus it has to choose what features and how they are represented at a given scalen taken into account the needs of the map users, the geographical data with its attributes and the readability of the map.
There are a lot of different methods that belong to cartographic generalization of which only a few are presented here.
Selection reduces the number of features by deleting features that are small or insignificant.
Simplification reduces unnecessary details by simplifying or abstrating shapes.
Smoothing refines and smooths geometries to make them more aesthetically pleasing.
Aggregation combines close features of the same type to a cluster.
Collapse reduces a features dimension and spatial extent.
Exaggeration increases the spatial extent of important and significant features.
Displacement resolves conflicts like overlaps by repositioning features.
Classification groups features into a new graphical representation.
Change the abstracted map by choosing above, which generalization methods to apply to it.