Editing Inverse distance weighting (section)

=== Historical reference ===
At the Harvard Laboratory for Computer Graphics and Spatial Analysis, beginning in 1965, a varied collection of scientists converged to rethink, among other things, what are now called [[geographic information system]]s.<ref>{{cite news |last=Chrisman |first=Nicholas |title=History of the Harvard Laboratory for Computer Graphics: a Poster Exhibit | url=http://isites.harvard.edu/fs/docs/icb.topic39008.files/History_LCG.pdf}}</ref>

The motive force behind the Laboratory, [[Howard_T._Fisher|Howard Fisher]], conceived an improved computer mapping program that he called SYMAP, which, from the start, Fisher wanted to improve on the interpolation. He showed Harvard College freshmen his work on SYMAP, and many of them participated in Laboratory events. One freshman, Donald Shepard, decided to overhaul the interpolation in SYMAP, resulting in his famous article from 1968.<ref name=shepardArticle>{{cite conference|last=Shepard |first=Donald |year=1968 |title=A two-dimensional interpolation function for irregularly-spaced data |book-title=Proceedings of the 1968 [[Association for Computing Machinery|ACM]] National Conference |pages = 517–524 |doi=10.1145/800186.810616|url=http://revistaseug.ugr.es/index.php/cuadgeo/article/download/5914/6786 }}</ref>

Shepard's algorithm was also influenced by the theoretical approach of [[William Warntz]] and others at the Lab who worked with spatial analysis. He conducted a number of experiments with the exponent of distance, deciding on something closer to the gravity model (exponent of -2). Shepard implemented not just basic inverse distance weighting, but also allowed barriers (permeable and absolute) to interpolation.

Other research centers were working on interpolation at this time, particularly University of Kansas and their SURFACE II program. Still, the features of SYMAP were state-of-the-art, even though programmed by an undergraduate.