The original reference is

Tobler, Waldo R. (1979), Smooth pycnophylactic interpolation for geographical regions, Journal of the American Statistical Association, 74, 367:519-530.

an adjustment for interpolation on the sphere is described in the NCGIA Technical Report TR95-6.

See also

Tobler, Waldo R. (1992), Preliminary representation of World population by spherical harmonics, Proceedings of the National Academy of Sciences of the United States of America, 89, 14:6262-6264.

For further information contact Waldo Tobler.

Back to population related projects at NCGIA.