What limitations can affect interpretation of choropleth cancer incidence maps?
When choropleth maps are presented, comprehensive cancer control decision makers should be reminded of the following constraints on interpretation: • Administrative-political boundaries reflect administrative-political needs and may have little relationship to the true spatial distribution of cancer incidence. • If a series of maps is prepared by using geographic units of analysis with different shape and area, the appearance of observed spatial patterns may appear to change. Geographers refer to this phenomenon as the modifiable areal unit problem (18). • Because choropleth maps fill the geographic unit of interest with the color corresponding to that unit’s rate, community decision makers may incorrectly assume that cancer rates are constant across the entire unit (19). For example, suppose the map shows cancer rates by county. Many US counties include neighborhoods with diverse characteristics (20). Consequently, for neighborhood planning, maps at the community level that apply more
