Skip common site navigation and headers
United States Environmental Protection Agency
EMAP-West Metric Browser
Begin Hierarchical Links EPA Home > Research & Development > Exposure Research > Environmental Sciences > Landscape Ecology > EMAP-West Metric Browser > Metrics > Human Stressors > Metric Map (rdlen), Natural Breaks, Methodology and Interpretation End Hierarchical Links


Metrics < Back | Top ^
 Metrics > Human Stressors > Metric Map (rdlen), Natural Breaks, Methodology and Interpretation
Detailed View
( PDF, 1 pp., 679 KB, About PDF )



<< Back

Methodology and Interpretation

RDLEN - Total road length
Total road length by class was calculated by summing the length of all road classes in the 3 km grid cell reporting unit. Values are reported in meters. The three road classes included were interstates, highways, and surface streets. Roads increase imperviousness, potentially decreasing water quality. Roads also fragment habitat and may act as barriers, especially to large mammals. Wider roads and higher traffic volumes will generally have more adverse affects, and impact a larger surrounding area then smaller, less traveled roads.

Metric Map (rdlen), Quantile Metric Map (rdlen), Natural Breaks

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.

Natural Breaks: Classes are based on natural groupings of data values. Natural break points are identified by looking for groupings and patterns inherent in the data. The features are divided into classes whose boundaries are set where there are relatively large jumps in the distribution of data values.

* EMAP-West Landscape Metrics Metadata (FGDC)


Overview | Metrics | Download | Contacts | Credits

Begin Site Footer

EPA Home | Privacy and Security Notice | Contact Us