The quality and scheme of shading or color on maps is of primary importance in making statistical maps an effective medium of visual communication. Plan shading and color schemes carefully, giving due consideration to the size or scale of the map, along with the amount of reproduction and reduction expected. A visual gradation in the shading or color from dense or dark to light is effective. This can be confusing to readers and blur the clear presentation of the data. Legend The ordering of colors or shading in a legend logically corresponds to the order of the range of values the coloring or shading represents, either from hight to low or vice versa.
Various colors represent the four categories.
They are the New England and Middle Atlantic States, Michigan and Illinois in the Midwest, Florida in the South, New Mexico and Arizona in the Southwest, and the Pacific States of California, Alaska, and Hawaii. The United States average revenue per kilowatthour in 1991 was 6.7 cents. Authors also could add, for example, a box with Census region or Census division averages. It is necessary to exercise care when using statistical maps to display data according to States or other political boundaries. Thus, area is proportional to the total rainfall.