Map Projections - Spatial Mathematics: Theory and Practice through Mapping - page 211

9.11.3 Internet café in Denver activity
In this exercise, you will have another opportunity to do some hands-on
work with map projections, using data that you worked with previously
to locate the optimal site for an Internet café in Denver. Creating areas of
proximity, or buffer zones, around points, lines, or areas is dependent on
the underlying map projection of those points, lines, or areas. Since the
buffer tools in GIS software use distances and areas to calculate and draw
the zones, the shape and size of the zones are affected by the map projec-
tion used. In the hands-on activity below, the shape and size of the areas
near schools and universities differ depending on the map projection used,
and hence, the parcels of land under consideration for the café will differ
depending on the projection used. A further item of interest is discoverable
from the use of GIS. GIS software will calculate buffer zones even when no
map projection is defined, based simply on distances in an x-y coordinate
space. But as we have emphasized repeatedly in this topic, great care must
be used in the interpretation and use of all mapped data. Unlike the North
Korean nuclear risk analysis example at the beginning of this chapter, here,
buffer zones based on unprojected data may only be slightly different from
those based on projected data when focusing on individual neighborhoods
in a city. But even at a local scale, the inclusion of certain parcels in or out
of the buffer zone takes time and money to consider, bid on, and site a
business.
Recall that in Chapter 3, when setting up the data for the Internet café
activity, you were asked to define the projection. This was done so that
buffer dimensions, that should be the same size independent of their loca-
tion on the map, would not vary depending on where they were placed.
The results were elliptical (non-circular buffers). Go back to those direc-
tions in Chapter 3 and repeat the exercise, this time failing to set the pro-
jection. Now, the buffers should be circular. Try setting the projection to
something other than either of the two above. The result, for this “local”
study, may show little difference from the WGS 84 that resulted in elliptical
buffers in Chapter 3. Projection matters—the more global the study, the
more it matters. Think about the situation that arose in the example at the
beginning of this chapter, with the global map of nuclear reach centered
on North Korea!
9.12 Related theory and practice: Access through QR codes
Theory
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