// cpt-city: usgs/usgs-feet (cpt)
//
// A land elevation scheme used by the U.S. Geological Survey
// with modified variants by Dr. Richard L. Langford for the
// Geological Survey of Western Australia
//
// author: U.S. Geological Survey, R. Langford
// copyright: Creative Commons Attribution-NonCommercial 3.0 unported
// year: 2021
// url: https://phillips.shef.ac.uk/pub/cpt-city/usgs
#declare usgs_feet =
color_map {
  [0.00000 color rgbf <0.4980,0.6235,0.3961,0.0000>]
  [0.02500 color rgbf <0.5098,0.6902,0.4392,0.0000>]
  [0.05000 color rgbf <0.6275,0.7608,0.4863,0.0000>]
  [0.10000 color rgbf <0.7255,0.8392,0.4863,0.0000>]
  [0.15000 color rgbf <0.8118,0.8784,0.6118,0.0000>]
  [0.20000 color rgbf <0.8745,0.9137,0.6588,0.0000>]
  [0.25000 color rgbf <0.9451,0.9333,0.6510,0.0000>]
  [0.30000 color rgbf <0.9294,0.8745,0.6235,0.0000>]
  [0.35000 color rgbf <0.9412,0.8235,0.5529,0.0000>]
  [0.40000 color rgbf <0.9020,0.7373,0.5412,0.0000>]
  [0.45000 color rgbf <0.8471,0.6471,0.5216,0.0000>]
  [0.50000 color rgbf <0.7725,0.5843,0.5294,0.0000>]
  [0.55000 color rgbf <0.8510,0.6471,0.6118,0.0000>]
  [0.60000 color rgbf <0.8902,0.7176,0.6941,0.0000>]
  [0.65000 color rgbf <0.8745,0.7529,0.7490,0.0000>]
  [0.70000 color rgbf <0.9373,0.8039,0.8510,0.0000>]
  [0.75000 color rgbf <0.9569,0.8431,0.8824,0.0000>]
  [0.80000 color rgbf <0.9529,0.8745,0.9137,0.0000>]
  [0.85000 color rgbf <0.9725,0.8902,0.9098,0.0000>]
  [0.90000 color rgbf <0.9725,0.9137,0.9333,0.0000>]
  [0.95000 color rgbf <0.9647,0.9412,0.9608,0.0000>]
  [1.00000 color rgbf <1.0000,1.0000,1.0000,0.0000>]
}