thumb|250px|Waldo Tobler in front of the Newberry Library. Chicago, November 2007
The First Law of Geography, according to Waldo Tobler, is "everything is related to everything else, but near things are more related than distant things." This first law is the foundation of the fundamental concepts of spatial dependence and spatial autocorrelation and is utilized specifically for the inverse distance weighting method for spatial interpolation and to support the regionalized variable theory for kriging. The first law of geography is the fundamental assumption used in all spatial analysis.
Background
Tobler first presented his seminal idea during a meeting of the International Geographical Union's Commission on Qualitative Methods held in 1969 and later published by him in 1970 in his publication "A Computer Movie Simulating Urban Growth in the Detroit Region".
While Tobler is the first to present the concept as the first law of geography, it existed in some form as a concept before him. In 1935, R.A. Fisher said "the widely verified fact that patches in close proximity are commonly more alike, as judged by the yield of crops, than those which are further apart." Tobler was made aware of this by a peer-reviewer, and seems to have come up with the first law independently. This law-making approach was conducive to the acceptance of Tobler's law, and Tobler's law can be seen as a direct product of the quantitative revolution.
In 2003, the American Association of Geographers held a panel titled "On Tobler's First Law of Geography", with panelists selected to represent diverse geographic interests and their philosophical perspective on Tobler's First Law. In 2004, the peer reviewed journal Annals of the Association of American Geographers included a section titled "Methods, Models, and GIS Forum: On Tobler's First Law of Geography" that contained several peer-reviewed papers from members of the 2003 panel. Of note, this section also had a paper by Tobler titled "On the First Law of Geography: A Reply", which contained his response to the 2003 panel and insight into the first law. or cost. For example, one is less likely to travel across town to purchase a sandwich than walk to the corner store for the same sandwich. In this example, hindrance, or cost, can readily be counted in time (amount of time as well as the value of time), transportation costs, and personal muscle energy loss which are added to the purchase price and thus result in high levels of friction. The friction of distance and the increase in cost combine, causing the distance decay effect.
Controversy
Some have disputed the usefulness and validity of Tobler's first law. In general, some also dispute the entire concept of laws in geography and the social sciences. These criticisms have been addressed by Tobler and others.