Look for complete geospatial metadata in this layer's associated xml document available from the download link

* Metric Name: Percent Impervious Surface *  

* Tier: 1  

* Data Vintage: 2019  

* Unit Of Measure: Percent, fractional imperviousness  

* Represent element and pillar: Yes  

* Type and distribution of data: Zero-inflated, right-skewed distribution representing percent values. Raw values range from 0 to 100.  

* Translation: Where is fractional impervious surface the lowest?  

* Translation method and outcome: Raw data values translated to range from +1 to -1 representing more favorable to less favorable conditions, respectively. **** The proposition of more favorable is based on the objective of low fractional impervious surface (negative linear slope). More favorable (translated to +1) set at 100, and less favorable (translated to -1) set at > 0\. 

Figure 76. Histogram and scoring of current condition of average annual mean
runoff across Southern California

Figure . Histogram of translated metric current condition of average annual
mean runoff across Southern California

Figure 214. Maps displaying raw metric and translated metric of current
condition of average annual mean runoff across the Southern California

  

* Metric Definition and Relevance: This National Land Cover Database (NLCD) product represents urban impervious surfaces as a percentage of developed surface over every 30-meter pixel of California, extracted from a nationwide layer. The definition of impervious means water does not seep into the ground, it runs off into storm sewers and then into local creeks. Examples of impervious surfaces include highways, streets and pavement, driveways, and house roofs. The relevance of impervious surfaces is the higher the proportion of impervious surfaces the more likely flooding can occur.  

* Credits: National Land Cover Database (NLCD) \--US Geological Survey, Earth Resources Observation and Science (EROS) Center