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( (http://www.confluence.org), ), photographically samples the Earth's graticule
at integer locations of parallels and meridians to create an archived inventory
of plants, animals, landforms, land use, and human impact at these locations.
Consider individual photos and reports of the set of discrete locations (Kerski
confluence visit at 42 degrees north latitude, 84 degrees west longitude, a
sample typical of such visits; Kerski, 2010). Each one gives an amount of geo-
graphic information confined by latitude and longitude within a small capsule.
When one is standing on the spot marking a degree confluence, projection
does not matter. Recall our earlier discussion on datum: Datum certainly mat-
ters because the datum used affects the position read by the GPS receiver.
Therefore, the position marking the intersection of the latitude and longitude
lines could be in a different meadow hundreds of meters away depending on
the datum used. But projection does not matter at this local scale. When one
wishes, however, to look at the whole set of confluences at a smaller scale,
projection does matter. As the Tissot ellipses mesh, as one moves poleward
in the sinusoidal projection of Figure 9.5 , so too do the integer latitude/lon-
gitude intersection points and associated photographic inventory. Converging
meridians, as one moves poleward, force this action.
In previous chapters, we have paid little attention to projection. For local
studies, projection considerations are not as important as they are for global
studies. As we function in the world, we are not generally aware of the cur-
vature of the Earth. A good general rule seems to be to choose the projection
that best fits your needs: If comparing landmass areas across the globe, for
example, choose an equal area projection. In global studies covering a broad
territorial expanse, projection selection can make a huge difference in the
portrayed outcomes.
9.9 Practice using selected concepts from this chapter
9.9.1 Overview
The material in this section presents an opportunity to view different maps,
cast in different projections, using dynamic maps in a web browser. This pro-
cess is done via live GIS mapping services in ArcGIS Online, a cloud-based
GIS used elsewhere in this topic. Here, the reader can use this platform to
map the location of global natural hazards, such as earthquakes, volcanoes,
and tsunamis, on different projections. By varying the projection, not only
do the differences in land and ocean patterns become apparent but so do the
interpretations of those patterns in relation to natural hazards.
9.9.2 Comparing projected data using ArcGIS online
To participate in this activity, go to ArcGIS Online ( http://www.arcgis.com/
home ). Click on the Groups tab and, in the search slot, type in the group name
“Projected Basemaps” (without the quotation marks. . .note that 'basemaps' is
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