Cultural sites located in the intertidal zone or close to the shoreline where they could be damaged by cleanup crews are at particular risk. Either such a location is shown within a polygon enclosing a larger area, or a map symbol is placed near but not exactly at the location. People using the ESI method to map human-use resources are encouraged to denote not only surface water intakes, but also groundwater recharge zones and well fields. Groundwater protection can be of particular concern when light petroleum products are spilled in rivers, and when wells are located in the floodplain and are hydraulically connected to the river. On ESI maps, each shoreline is color-coded to indicate its sensitivity to oiling.
Warm colors indicate the most sensitive shorelines, and cool colors indicate the least sensitive.
Large habitat areas, such as tidal flats and wetlands, are shown as polygons filled with a pattern of the appropriate color. Most biological resources are represented on ESI maps by polygons, which encompass larger areas where particular species exist. Fish streams are usually represented as lines. The point symbols, polygons, and lines representing different kinds of animals are color-coded. Most human-use features exist in a small area and are represented by point symbols .