Methodology and Interpretation
The percentage of cropland cover is calculated by dividing the number of cropland land cover
cells in the reporting unit by the total number of land cover cells in the reporting unit minus
those cells classified as water (i.e., total land area). Agricultural practices typically employ
fertilizers, pesticides and other chemicals that may be transported to streams in water runoff.
The closer agriculture is to a stream the more likely related pollutants will enter the stream.
Concentrations of pollutants transported into streams are also more likely to be higher when
agriculture is closer to streams.
Quantile: Each class contains an approximately equal number (count) of features. A quantile
classification is well-suited to linearly distributed data. Because features are grouped by the number
within each class, the resulting map can be misleading, in that similar features can be separated into
adjacent classes, or features with widely different values can be lumped into the same class. This
distortion can be minimized by increasing the number of classes.
Metric input GIS data:
- United States Hydrologic Units (8-digit HUCs) - Metadata
- United States Coastal Change Analysis Program (CCAP) - Metadata
- Canada Hydrologic Units (Subsubdivisions) - Metadata
- Ontario Ministry of Natural Resources Data Set - Metadata