EARTH AND SPACE SCIENCE

Chapter 3 Models of the Earth

3.2 Mapping Earth’s Surface

3.2 Mapping Earth’s Surface Objectives

• Explain two ways that scientists get data to make maps.

• Describe the characteristics and uses of three types of map projections.

• Summarize how to use keys, legends, and scales to read maps.

Introduction

• A globe can accurately represent locations, relative areas, and relative shapes of Earth’s surface features since the globe is spherical – like the Earth!

• The finer details of Earth’s surface cannot be accessed using a globe.

How Scientists Make Maps

• Cartography is the science of making maps.• Cartographers are scientists who make maps.• Cartographers use data from a variety of

sources in order to make maps.– Field Survey – cartographer walks or drives through

an area and takes measurements to be plotted on a map

– Remote Sensing – images of the Earth taken from a plane or satellite are used to make maps

– Combination of field surveys and remote sensing are often used to map an area

Map Projections

• A map is a flat representation of Earth’s curved surface.

• Distortion in size, shape, distance, or direction may occur when transferring a curved surface area to a two dimensional map.

• The larger the area represented on the map, the greater the distortion tends to be.

Map Projections

• A map projection is a flat map that represents the three-dimensional curved surface of Earth.

• Though no projection is entirely accurate, some types of projection maps are more useful to us than others.

Map Projections

• Cylindrical (Mercator) projections are constructed with straight meridians and appear as if someone put a lighted globe in the middle of a paper cylinder with the paper only touching at the equator.

• This map is accurate at the equator, but distorts size and distances near the poles.

• Locating positions is easier on this type of map because of the grid created by making the meridians parallel.

• The mapping of small areas is done this way because distortion of those areas is minimal.

Map Projections

• Azimuthal (Gnomonic) projections are made by putting a sheet of paper against a transparent lighted globe such that the paper touches the globe at only one point.

• Very little distortion occurs at the point of contact on this type of map, yet the distortion increases as you move away from the point of contact.

• Azimuthal projections show unequal spacing between parallels which results in distortion of distances and directions.

• Azimuthal projections are useful for navigators to plot routes for air travel because drawing a straight line on an azimuthal projection is the shortest distance between two points on a globe.

Map Projections

• A conic projection is made by placing a paper cone over a lighted globe so that the axis of the cone aligns with the axis of the globe.

• The cone touches the globe at one parallel of latitude.

• Distortion is minimal at the point where the cone touches the latitude of the globe.

• Polyconic projections, a series of conic projections used to make a map, are used to minimize distortion.

Reading a Map

• In order to read a map, one must be able to understand symbols and figure direction and distance.

• Most maps are made so that north is at the top, east to the right, west to the left, and south to the bottom.

• Lines of longitude are often parallel as well as lines of latitude being parallel.

• A compass rose often is used to determine direction on the map.

Reading a Map

• Maps with multiple symbols will often have a legend – an explanation for what the symbols mean.

• The scale of a map shows the relationship between the distance on the map and the actual distance.– Graphical scale – marked line similar to a ruler that

will be of a specified distance– Fractional (ratio) scale – mathematic representation

of the relationship, often a ratio of map distance to actual distance

– Verbal scale – verbal expression of the distance relationship between the map and actual area

References

• Globe - http://www.library.yale.edu/MapColl/globes.html

• Topographic Map - http://www.adirondacknorthway.net/mappages/mount_marcytopo.php

• Cylindrical Projection Map - http://www.3dsoftware.com/Cartography/USGS/MapProjections/Cylindrical/MillerCylindrical

• Cylindrical Projection - http://www.cnr.colostate.edu/class_info/nr502/lg1/map_projections/form_case_aspect.html

References

• Azimuthal Projection - http://www.cnr.colostate.edu/class_info/nr502/lg1/map_projections/form_case_aspect.html

• Azimuthal Projection Polar Map - http://www.3dsoftware.com/Cartography/USGS/MapProjections/Azimuthal/Gnomonic

• Polyconic Projections - http://www.nationalatlas.gov/articles/mapping/a_projections.html

• Conic Projection - http://www.yourdictionary.com/ahd/c/c0570900.html

References

• Compass Rose - http://cuip.uchicago.edu/~tjones/home/science/eq/page8.html

• Map Scale - http://cropsoil.psu.edu/Courses/Soils101/lectures/MapScale/MapScale05.html

• Map Legend - http://www.dot.state.oh.us/map1/ohiomap