Exercise 5: Map Projections

How does the Eckert maintain equivalence in the high latitudes (what happens to the meridians)?

Meridians converge toward the poles.

On a globe, the meridians converge toward the poles. Describe the pattern of meridians on the Mercator.

Meridians do not converge, they run straight up and down on the map.

Do all of the parallels and meridians cross each other at right angles?

No

Could a single graphic scale be used to measure distances on a Mercator projection? Explain.

No, distance scale changes toward the poles.

Is north always straight toward the top of the Eckert? Explain.

No, need to follow meridians around toward the North Pole.

Are all of the lines of latitude parallel to each other on both the globe and the Mercator projection?

Yes

Do all of the parallels and meridians cross each other at right angles on both the globe and the Mercator? (Hint: Look carefully at just the immediate intersection of a parallel and a meridian on the globe.)

Yes

Is north always straight toward the top of the Mercator projection?

Yes

Study the Goode's Interrupted projection (Figure 5-6): a) Are ocean areas "left off" this map? Explain. b) The Goode's is based on two different projections, one for the low latitudes and one for the high latitudes. At approximately what latitude does the projection change? (Hint: Look for the change in the shape of the map margins in the North Pacific.)

a) No, the map is only interrupted (pulled apart) in the oceans. b) About 40° N and S.

How would the North Pole be represented on the Mercator?

A straight line.

How would both a Mercator and a Gnomonic map be used together in navigation?

Gnomonic used to determine the shortest route; Mercator used to plot a series of rhumb lines to closely follow great circle route.

What happens to the shape of Greenland?

It is extremely distorted in size and shape.

On a globe, use a piece of string to find the shortest path between Yokohama, Japan (near Tokyo) and San Francisco. This path is a "great circle" path. Two maps are shown here, a Gnomonic and a Mercator. a) Is the path of the string on your globe the same as the heavy line shown on just one of these maps, or on both of these maps? (Hint: Look carefully at the string on the globe in relation to the Aleutian Islands of Alaska [at about 50° N, 175° W].) b) In terms of a navigator trying to maintain a constant compass heading, why would the great circle path shown be difficult to follow exactly?

a) Path is the same on both maps. b) Compass heading (direction) changes constantly.