Cartograms or statistical maps are used to give quantitative information on a geographical basis. They are thus used to represent spatial distributions. The quantities on the map can be shown in many ways, such as through shades or colour, by dots, by placing pictograms in each geographical unit and by placing the appropriate numerical figure in each geographical unit.
Statistical maps should be used only where geographic comparisons are of primary importance and where approximate measures will suffice. For more accurate representation of size, bar charts are preferable. To be sure, maps are sometimes combined, which are drawn in the appropriate areas.