Mapping The Past: Annexations and GIS

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Keeping a record of the past is important to help give those in the
present and future a better idea of how their current surroundings
developed. Whether these surroundings are cultural, political, or
genealogical, tracking the history of each can be a way to maintain a
connection to where an individual or group of individuals came from. The
same holds true for municipal entities, which can track the historical
development of their political boundaries using annexation records that
are maintained over time.

For Des Plaines, annexations are approved based on a series of legal
sheets describing the boundaries of each area. While these are useful
for court cases and in regulating land disputes, it can be difficult to
get a sense of how the community developed by reviewing each document
individually. To help get a comprehensive view of the city’s boundary
development, the GIS department began tracking these areas in a GIS
system to provide both an analytical tool and a means to develop a
mapping product that can be provided to city departments. As an
analytical tool, other city GIS data layers can be used in conjunction
with the annexation information to help answer a variety of capital
asset-related questions such as the age of utility mains and potential
roadway resurfacing schedules. As a mapping tool, having the annexation
information in GIS allows for spatial products to be created that allow
for city departments, alderman, and, potentially, residents to see how
the city developed over time.

Integrating annexations into the city’s GIS system has taken detailed
legal descriptions of annexation plats and converted them into a more
digestible, visual format for review. This makes understanding the
boundaries of these annexation areas easier, which can lead to faster
and more efficient decision making.