A Beginner's Guide to Geographic Virtual Communities Research devices and web-based APIs, and therefore is the most common datum behind latitude and longitude coordinates. However, with the advent of Google Earth, a new datum has risen in popularity: the Google Earth datum. The Google Earth datum deviates from WGS84 due to a problem called (satellite) image misregistration. Goodchild (M. F. Goodchild, 2007) found that in Santa Barbara, California, this error will cause positioning to be off by about 40 meters. Google Earth image misregistration also affects any geographic data layer made using Google Earth as a reference. Depending on what type of project the reader has in mind, the above two paragraphs should result in one of two reactions: 1. 2. 40 meter error? Why do I care about 40 stinkin' meters? 40 meter error! That ruins my whole project! more than one dimension. Spatial autocorrelation is so important to the study of geographic infor- mation that it is described in the so-called First Law of Geography 15 : "everything is related to everything else, but near things are more related than distant things"(Tobler, 1970). While it is well beyond the purview of this chapter to explain this phenomenon in detail (spatial statistics is the field that focuses on spatial autocorrelation issues), it is important that "geo- novices" be aware of spatial autocorrelation. In particular, the virtual communities researcher should know that spatial autocorrelation can cause a violation of the standard independent and identically distributed (iid) assumption of regression error terms. According to de Smith and colleagues, "many (most) spatial datasets exhibit patterns of data and/or residuals in which neighboring areas have similar values (positive spatial autocorrelation) and hence violate the