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magnetic poles. The north magnetic pole is located in the Queen
Elizabeth Islands group, in the Canadian Northwest Territories.
The south magnetic pole lies near the edge of the continent of
Antarctica, off the Adélie Coast. The magnetic poles are constantly
moving. What are the implications of this fact for the stability of
our graticule?
In the following section, you will have the opportunity to work with measure-
ment, the graticule, and with map projections using a variety of web-based
GIS tools.
2.10 Practice: Work with measurement, the graticule, and
map projections
In this section, you will have the opportunity to measure units off of the grati-
cule using a web-based GIS. Open a web browser and access
www.arcgis.com
(ArcGIS Online). In the search box, enter “World Relief Map for Schools” and
open it. Zoom out until you see the lines of latitude and the lines of longi-
tude represented in a spacing of 15 degrees apart. On a map in the Mercator
projection, such as this, notice that the lines of latitude and longitude are
represented as straight lines. We will discuss map projections in detail in a
later chapter, but notice how the lines of longitude are spaced evenly while
the lines of latitude get farther apart as one approaches the North Pole and
the South Pole. What do you notice about the sizes and shapes of land masses
near the North Pole and the South Pole? Why do you suppose these distor-
tions occur? The sizes and shapes become distorted near the poles because of
the fact that any map has to distort the bounded curved surface of the Earth
onto an unbounded flat paper or digital map.
Verify the numeric value of the latitude and longitude lines by clicking on
each of them. Select the tool that shows the individual map layers that make
up your map, and expand the graticule layer several times to see that this
layer is actually composed of several layers, as shown in
Figure 2.4
.
These layers are scale dependent. As you zoom in, a finer, higher resolution
mesh of latitude and longitude lines appears. Zoom to the Equator in South
America by holding the Shift key and simultaneously dragging a box with the
mouse. Or, search for Quito, Ecuador, and find the Equator nearby. What is
the finest mesh of latitude and longitude lines that appears? According to this
map, it is a one degree mesh. Consider the discussion of latitude and longi-
tude reference lines earlier in this chapter. Is the latitude-longitude grid you
are now examining the finest mesh that could be generated? Why or why not?
There are an infinite number of finer graticules that could be generated; for
example, a half-degree, 10 minute, or even one second mesh.
Use the measure tool to find the distance between one degree of longitude and
the next degree of longitude to the east or west. Indicate the units you have
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