How should information about reliability (eg, unstable rates) be displayed on a map?
Several methods exist to display information about reliability of rates on a map. One option uses different shades of gray to indicate map areas with small numbers, unstable rates, or missing data. If colors are used to indicate areas with stable rates, areas shaded gray tend to remain in the background. A second option employs hatched lines to convey rate variance. The hatched lines allow the underlying spatial patterns to be seen. The Atlas of United States Mortality (15) illustrates how double-hatching with parallel white and black lines can be used over light and dark colors. A third method, proposed by Carr and colleagues (28,29), provides confidence intervals in addition to mapped rates. The mapped rates are ranked, confidence intervals are calculated around each rate, and a graph of the ranked rates with their confidence intervals is then displayed adjacent to micromaps of the rates. This approach is used in the Comparative Data Display section of the State Cancer Profiles (9).
