(Aid to helping you analyze the sources of map error, rather than just describing maps as "good" or "bad.")

1. OBSERVATION OR SAMPLING PROBLEMS - These occur when someone makes a mistake in gathering information.

2. DATA TRANSFORMATION PROBLEMS - These occur when someone uses the wrong calculation and the resulting percentages, densities, or some other ratio was not appropriate.

3. SYMBOL SELECTION PROBLEMS - These occur when a cartographer uses an inappropriate symbol to display some information.

4. SYMBOL PERCEPTION PROBLEMS - These occur when a map reader misreads a symbol because of an optical illusion or a confusion with nearby symbols.

5. PROJECTION PROBLEMS - These occur when someone tries to show a big part of the curved earth on flat paper. This cannot be done without distorting something: shape, size, connection, and/or direction.