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set of items arranged in a fashion where it is possible to state, with certainty,
that any given item is “above,” “below,” or “at the same level as” any other
element in the set. Most military organizations have a clear-cut hierarchy of
ranks of officers. Often churches, universities, and other institutions have
hierarchies of administrators or professional staff. The certainty afforded by a
hierarchy offers ease and effectiveness in communication.
There are, however, situations in which hierarchies can be problematic. As
long as a hierarchy is “nested,” where a large polygon is composed of small
polygons that fit within the large one in some systematic manner, there is no
loss of clarity in interpretation. When hierarchies formed on different nesting
principles are superimposed, it can become impossible to extract clear mean-
ing in the underlying data. In
Figure 7.1
, the county boundaries fit together
with no overlap and cover the entire state exactly. The school districts form
a nested hierarchy with smaller polygons filling larger ones with no overlap.
Look within the circle superimposed on that map. The oddly-shaped school
district overlaps three different counties (with rectilinear boundary lines).
When these two nested hierarchies are superimposed, the meaning is lost.
One cannot tell how to assign the residents of a county to a school district
when there is ambiguous information! Clearly, it is important to create nested
hierarchies and to do so in the broad context of considering how other related
hierarchies are being created!
Figure 7.1 County/state boundary hierarchy does not mesh with school district
boundary hierarchy. One example is highlighted inside the circle. Look for oth-
ers, especially in the northwest region of the map. Source: “School Districts and
gov
, produced by: J. Shively, Michigan Center for Geographic Information,
michigan.gov/documents/CGI-state_sch_district_67407_7.pdf
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