Number of classes Normally, no more than 5-7 groupings should be portrayed. Otherwise, most users will constantly have to refer to a legend or chart to understand. The problem of class boundaries. Class limits-discrete vs. continous data. Cartographers have developed many methods to define and portray class limits.
Improper selection can present misleading or worse, false information.
Cutpoints-how we divide and portray the data. Equal steps, quantiles, percentages, arithmetic, geometric, standard deviation, and inverse methods. Simplification of data-one cannot put everything about a particular environment on a map. Scale, purpose, and data availability define. For example, if we are illustrating the vegetation of Texas we cannot illustrate buildings without making the map totally useless.