Researchers in the field of Geographic Information Systems (GIS) use large data sets, many of which are combined with additional data sets to analyze and display information. Data relating to research is usually collected in the field and combined with layers of data from other sources. These sources are often credited within the text of an academic paper, but are not reported in the list of references. Citation of data is important in order to acknowledge and validate the source, and to create ease of access for other users. This study assesses the rates of GIS data citation in a sample of peer-reviewed academic journal articles from the years 2002 and 2012 to illuminate trends in citation patterns.