Class "Density" is an S4 class containing a list of grids which
describe the density of individuals / clusters of a population. The list
contains one grid (data.frame) for each strata.
region.nameObject of class "character"; the region name.
strata.nameObject of class "character"; the strata names
density.surfaceObject of class "list"; list of data.frames
with the columns x, y and density. There must be one data.frame for each
strata.
x.spaceObject of class "numeric"; The spacing between
gridpoints described in the density data.frames in the x-direction.
y.spaceObject of class "numeric"; The spacing between
gridpoints described in the density data.frames in the y-direction.
unitsObject of class "numeric"; The units of the grid
points.