A ZIP code map with rainfall history data shows the average rainfall over a specified period of time. The rainfall overlay demonstrates the rainfall distribution, so you can learn which areas of the ZIP code get the most rainfall. If the map features a topography layer, you can also learn how rainfall averages vary from high points to low points.
Most rainfall history maps use color overlays to show rainfall throughout a ZIP code area. Each color corresponds to an amount of precipitation; the scale is laid out in a key to one side of the map. Because rain does not fall within neatly defined areas, the borders between different rainfall areas are approximations.
The base map of a rainfall history map impacts the information it contains. A standard street map simply explains rainfall based on location. A satellite base map shows landforms and bodies of water, and it helps readers understand how geography affects precipitation. A topographic base map explains how rain levels vary at different elevations.
The date range you choose for a rainfall history map impacts the things you can learn. In a ZIP code with wet winters and dry summers, the rainfall map looks markedly different in July than it does in January.