To demonstrate the challenge of moving from 3-D to 2-D with a sphere, invite volunteers to the front of the room and give each a navel orange or other type of orange that is easily peeled.
Ask them to peel the orange, trying as best they can to keep the peel in one piece. One at a time, place the peels on an overhead projector and discuss the shapes as a whole class. Have them imagine this is the surface of Earth or a globe. Show the video, The Cartographer's Dilemma, to introduce the challenges that cartographers face with representing Earth on a flat surface.
Tell students they will next test the reverse, changing from a flat map to 3-D. Divide students into small groups of three. Give each group one copy of the 3-page worksheet Map to Globe: 2-D to 3-D Models, scissors, and transparent tape.
Have groups study these versions of the globe. Ask: What is the relationship between lines of longitude and the black lines cuts on the map? The cuts are all made along lines of longitude.
What is the relationship to the Equator? Cutlines stop at the Equator. Have each member of each group work with one page to cut and tape together a model, attempting to make a globe from the maps. Project the three maps Mercator, Mollweide, and Robinson showing different map projections that have been developed by cartographers. Read the captions for each. Ask: What do you observe about the lines of longitude in each of these map projections? Some have lines of longitude meeting at the poles; some have parallel lines of longitude; some have curved lines of longitude but do not meet at north and south poles.
Have students analyze the three projections and the globe to note the distortions found. Have students also compare the size that area is proportional and the shapes of land and water on the maps with what they see on the globe.
You may want to show this short video more than once. Allow students to revise their findings based on this information. Have students refer to the Map Projections handout, and use the provided answer key to have a whole class discussion about their answers in the chart. Next, project the upside-down map of the world and the Pacific-centered world map. Does it matter if a continent is larger or smaller in relation to other continents and on the map and on the globe?
Have them debate what they believe is the best map for use in classrooms and the general media, such as news reporting. Many maps were a work of art and the essential map elements were there to make it useful to the end users.
I am truly amazed looking back at the maps produced by the early explorers, like Captain James Cook who mapped Australia over years ago. They mapped the coastline from their ships using what we might called primitive tools but it was amazing how accurate they were.
Today we just pull up the latest satellite image, assuming that it has been rectified correctly and is fit for purpose. Know why you are producing the map, know why the data was captured. Take the time to bring out the cartographer in yourself. Save my name, email, and website in this browser for the next time I comment. Geoawesomeness is a blog about geospatial technologies and everything awesome around it.
We are passionate about gis, maps, location-based apps, geomarketing, drones and remote sensing. Any line you measure on this globe—no matter how long or in which direction—will be one forty -millionth as long as the corresponding line on the earth. In other words, the scale is true everywhere. This is because the globe and the earth have the same shape disregarding the complication of sphere versus spheroid.
Now suppose you have a flat map that is 40 million times smaller than the earth. See the problem coming?
Instead of comparing a big orange to a little orange, we're comparing a big orange to a little wafer. This map also has a scale of ,,, but because the map and the earth are differently shaped, this scale cannot be true for every line on the map.
The stated scale of a map is true for certain lines only. Which lines these are depends on the projection and even on particular settings within a projection. We'll come back to this subject in Module 4, Understanding and Controlling Distortion. Not all of the earth's curves can be represented as straight lines at the same fixed scale.
Some lines must be shortened and others lengthened. Expressing map scale There are three common ways to express map scale:. Linear scales Linear scales are lines or bars drawn on a map with real-world distances marked on them.
To determine the real-world size of a map feature, you measure it on the map with a ruler or a piece of string. Then you compare the feature's length on the string to the scale bar. A typical scale bar. Verbal scales Verbal scales are statements of equivalent distances.
For example, if a 4. Representative fractions Representative fractions express scale as a fraction or ratio of map distance to ground distance. Since the scale is a ratio, it doesn't matter what the units are.
Small scale and large scale maps It's easy to mix these terms up. Here's one way to keep them straight: on a large-scale map, the earth is large so not very much of it fits on the map. On a small-scale map, the earth is small so all or most of it fits on the map.
All in all, it is up to the cartographer to determine what projection is most favorable for its purpose. When you place a cone on the Earth and unwrap it, this results in a conic projection. Both of these map projections are well-suited for mapping long east-west regions because distortion is constant along common parallels. But they struggle at projecting the whole planet.
While the area is distorted, the scale is mostly preserved. For conic map projections , distance at the bottom of the image suffers with the most distortion. When you place a cylinder around a globe and unravel it, you get the cylindrical projection.
Strangely enough, you see cylindrical map projections like the Mercator and Miller for wall maps even though it inflates the Arctic. You can place it in a vertical, horizontal or oblique position such as the State Plane Coordinate System.
Each one has its own use in mapping the world. These types of projections plot the surface of Earth using a flat plane. Similar to light rays radiating from a source following straight lines, those light rays intercept the globe onto a plane at various angles. The light source can be emitted from different positions developing different azimuthal map projections.
For example, gnomonic, stereographic, and orthographic are common azimuthal projections. Remember that with a sphere, we use latitude and longitude to pinpoint our position. This is our geographic coordinate system. But when the Earth has a map projection, this means that it has projected coordinates. For example, the Universal Transverse Mercator system splits the Earth into 60 sections by lines of longitude.
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