Goals of Cartography and GI: Representation and Communication - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 15

The map on the left shows current road status (events), the map on the right
shows highway projects (things) that can affect traffic. Each map uses a different cartographic rep-
resentation as well.
From www.dot.state.mn.us/tmc/trafficinfo/map/refreshmap.html and www.511mn.org/
default.asp?area=TC_Metro . Reprinted by permission of Mn/DOT.
for anyone to make a map of everything in the world; nor is it possible to
make a map of any area showing everything at that place, even at just one
time. Every map is an abstraction that focuses on a selection of things and
events from that place according to the purpose of the map. A highway map
emphasizes roads and represents buildings, rivers, and towers in the land-
scape as context for using the map to navigate. A map of forest fires shows
the location of fires and represents the slope and exposure of the hills or
mountains with contour lines.
Geographers and cartographers want these representations to be reli-
able for the purpose they are intended for. A highway map is good for driv-
ing in a car; it is less useful for riding a bicycle and of little use for planning a
trail hike in a state park. The maps of forest fires in a national park are good
for understanding where forest fires occurred, but may be less helpful to
determine why the fires occur and where they may occur in the future, and
not of much use at all when planning a hike.
The reliability of a map or geographic information depends greatly on
the choices made in abstracting things and events to the static patterns
shown on a map or the information stored on a computer. Following Nick
Chrisman, these choices are part of a framework encompassing measure-
ments that record aspects of geographic things and events; representation of
these measurements as geographic information to indicate geographic
things, events, and associations; operations on these measurements to pro-
duce more measurements; and transformations of the representations to
other frameworks. The integrity of the process of representation makes for
reliable maps and geographic information. You will see later how this