archimedean.rb

require 'json'

def get_lonlat_in_spiral(i)
  v = Complex.polar i, i/4.9 * Math::PI/2
  angle = v.angle
  magnitude = v.magnitude
  [magnitude * Math.cos(angle), magnitude * Math.sin(angle)]
end

r = 10.upto(30).map { |i| get_lonlat_in_spiral(i) }

coords = r.map {|x, y| [139.6 + y * 0.01, 35.7 + x * 0.01] }

puts JSON.generate(
  type: "MultiPolygon",
  coordinates: [coords.map {|y, x| [y.floor(5), x.floor(5)] }.map { |y, x|
    [
      [y, x],
      [y, x + 0.01],
      [y - 0.01, x + 0.01],
      [y - 0.01, x],
      [y, x]
    ]
  }]
)

result.geojson