def contours(<EOL>self, elevation, interval=<NUM_LIT:100>, field='<STR_LIT>', base=<NUM_LIT:0><EOL>):
return commons_contours.extract_contours(<EOL>elevation, self.tile, interval=interval, field=field, base=base)<EOL>
Extract contour lines from elevation data.

Parameters
----------
elevation : array
    input elevation data
interval : integer
    elevation value interval when drawing contour lines
field : string
    output field name containing elevation value
base : integer
    elevation base value the intervals are computed from

Returns
-------
contours : iterable
    contours as GeoJSON-like pairs of properties and geometry