Geometry of the Sphere - Spatial Mathematics: Theory and Practice through Mapping - page 24

to be in order to draw? The letters have to be at least this high for the shapes
to be discernible. If they are anything smaller, the GPS would not be able to
distinguish the angles of the letters necessary to read them.
1.6.3 Great circle routes
In this section, you will have the opportunity to practice with great circle routes
using a web-based GIS and with a GPS receiver or smartphone. You will start
by measuring distances and thinking about great circle routes as you do so.
First, use a web-based GIS, ArcGIS Online, ( www.arcgis.com/home ) that you
used in the above activity. Start a new map by selecting “map.” Zoom out until
you can see London, England, and Los Angeles, California. Access the mea-
sure tool and click on the measure line symbol. Set the distance units to miles
or kilometers—whichever you prefer. Click on Los Angeles and then click on
London, as shown below (Figure 1.16).
Why is the shortest line distance from Los Angeles to London shown as an arc?
What is another name for this arc? The shortest distance is shown as an arc
because the Earth is a sphere, and the shortest distance between two points
is an arc on that sphere, known as a great circle. What countries and land
masses does your arc touch, and therefore, which countries would you see if
you were on an airline flight between the two cities? You pass over Canada,
Figure 1.16 The shortest distance from Los Angeles to London. Source of base map:
Esri software.