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Geology LibreTexts

2.4: Map Scale and Projection

Map scale is defined as: The ratio of distance on a map to distance on the ground Map scale is generally expressed as a ratio, such as 1:100,000. This means that one unit on the map is equal to 100,000 units on the ground, or the map representation of a widget is 1/100,000th of the actual size of the widget.

One way that I find useful to visualize map scale is to think about a map of the world. The length of the equator at different scales is a good way to think about the actual size of a map at that scale. The table below lists the distance on the map (as if you were to lay a ruler along the map and measure the equator) for each map scale. As you can see, a 1:400,000,000 scale map would probably fit across two pages of your textbook, while a 1:10,000,000 scale map would take up a wall of your classroom. At 1:1,000 scale, a map of the world would stretch across the county!

The Length of the Earth's Equator at Different Map Scales

Map Scale
Distance of the Equator on the Map (m)
1:400,000,000
0.10002
1:40,000,000
1.0002
1:10,000,000
4.0008
1:1,000,000
40.008
1:100,000
400.078
1:10,000
4000.78
1:1,000
40,007.8

Large Scale Maps vs. Small Scale Maps

“Large Scale”

 

 

Small features are large

  • A map of this room
  •  

    A map of this campus

     

  • A map of this city

“Small Scale”

 

 

Large features are small

 

  • A map of this country

     

  • A map of this world
 

Resolution is defined as: The smallest feature that is represented on the map

  • A city such as Los Altos Hills probably would not be represented on a map of the USA (at a scale 1:10,000,000). The resolution of this map is therefore too coarse to represent our city.
  • A city such as Los Altos Hills probably would be represented on a map of the Bay Area (scale 1:500,000). The resolution of this map is therefore fine enough to represent our city.

Map projection is the way in which we represent the spherical earth on a flat map (see below). You may want to do some searches to find different types of map projections. The most important thing to remember about map projections, however, is that there will always be some distortion. Some map projections preserve relative areas, some projections preserve shape (such as the shape of coast lines), some try to do both and end up doing neither. But the result is that there will always be some error in a projected map.

 

Figure 2.4.1 Map projection

One example of error in map projection can be seen in maps of the United States. The graphic below shows three different projections of the United States overlain. Note that the further you get from the center of the projection (the hot pink dot in the middle of the figure below) the bigger the distortion gets. Look in particular at Florida, Washington and Maine.

Figure 2.4.2 Map projection of the United States

Another example of distortion caused by map projection is the represented area of Australia and Greenland. The landmass of Greenland is 1/3 that of Australia. That is to say, Australia is three times as big as Greenland. The map on the left is a Mollweide Equal Area projection which preserves the relative area of landforms. The projection on the right is a Gall projection (very similar to a Mercator projection), and it preserves the shape of landforms but not the area.

    

Figure 2.4.3 More map projections

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