Organized activity by which people measure and represent geographic phenomena
then transform these representations into other forms while interacting with social
structures (Chrisman, 1999).
Nicholas Chrisman developed this definition as an attempt to address
the open questions about Duecker's and Kjerne's definition (and many oth-
ers—see chapter readings—that express the same main concepts as their defi-
nition). Chrisman's definition focuses on the activities of measuring and rep-
resenting in the context of social structures. This is the short form of a more
involved conceptual model of GIS which consists of a nested set of rings and
interactions between the rings.
Chrisman's “shell model” of GIS is broad and inclusive. In its focus on
activities, it points to the importance of knowing what any particular GIS is
used for. Operations (common GIS processes) and transformations (pro-
cesses that change the measurement framework) are the emphasis in
Chrisman's discussion of how GIS is used. In the redrawn and modified ver-
sion of the “shell model” figure, the emphasis is placed on activities that are
essential to the successful development and use of any GIS. First, data qual-
ity involves verifying measurements and geographic representations in com-
parison to the corresponding things and events found in the world. Second,
the operations and transformations used in any GIS need to undergo an
evaluation of each and every use of the GIS. Finally, conventions originating
in society, culture, and institutions require consideration to assure that the
data accurately correspond to the things and events and the operations and
transformations take into account the goals of the GIS.
System of computer hardware, software, and procedures designed to sup-
port the compiling, storing, retrieving, analyzing, and display of spatially ref-
“Shell model” showing elements of GIS and interactions
Source: Chrisman (1999). Adapted by permission.