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 - ml ml Topographic Map - /mount_marcytopo.php /mount_marcytopo.php Cylindrical Projection Map - S/MapProjections/Cylindrical/MillerCylindrical S/MapProjections/Cylindrical/MillerCylindrical Cylindrical Projection - g1/map_projections/form_case_aspect.html g1/map_projections/form_case_aspect.html

References Azimuthal Projection - g1/map_projections/form_case_aspect.html g1/map_projections/form_case_aspect.html Azimuthal Projection Polar Map - S/MapProjections/Azimuthal/Gnomonic S/MapProjections/Azimuthal/Gnomonic Polyconic Projections - a_projections.html a_projections.html Conic Projection -

References Compass Rose - ience/eq/page8.html ience/eq/page8.html Map Scale - lectures/MapScale/MapScale05.html lectures/MapScale/MapScale05.html Map Legend - p p