Individual value themes show points, lines, or boundaries that are shaded by individual values contained in a particular field or the result of an expression. You can use both numerical and nominal values in individual values maps. Each unique value is given its own color or symbol. When an individual values map uses symbol types, the symbols are taken from the base table.
If you are shading your points, lines or boundaries using nominal data, you can shade only by individual values. Nominal data is either non-numerical data (name, type of cuisine served, or brand of automobile sold) or numeric data where the numbers represent non-numeric data like an ID number. Dates are considered numeric data and can be used in both ranged and individual values maps.