Maps and Map Projections. How Maps Can Mislead Us

Size: px

Start display at page:

Download "Maps and Map Projections. How Maps Can Mislead Us"

Patricia Osborne
7 years ago
Views:

1 Maps and Map Projections How Maps Can Mislead Us

3 A Globe Is the only truly accurate representation of the earth

4 A flat surface It is easy to portray a flat surface on a flat piece of paper

5 But there is no way to accurately portray a 3-dimensional round surface on a flat piece of paper Therefore all maps are distorted

6 Distortion will occur in at least one of these map components: Size (area) Shape Distance Direction

7 Making Maps Mapmakers have devised many different methods for making maps of the world

8 Projections The different methods are called projections The term projection refers to projecting the 3-dimensional globe onto a flat surface

10 Equivalent A map that is equivalent is accurate in size or area It is NOT going to be accurate in shape

11 Peter s map is equivalent

12 Conformal A map that is conformal is accurate in shape It will NOT be accurate in size (area)

13 Mercator map is conformal

14 A world map cannot be both equivalent and conformal Equivalence and conformality are mutually exclusive properties

15 Common Map Projections Cylindrical Conical Planar or polar Compromise

17 Tangency Each projection is accurate at the point(s) of tangency only Cylindrical: equator (line) Conic: mid latitude (line) Planar: one pole only (point) Further away from point(s) of tangency = more distortion

18 Cylindrical

19 Cylindrical Projections Common for world maps Distorts size (area) more in areas farthest away from the equator Distortion greatest in northern latitudes most of the northern hemisphere s land mass is far from the equator Mercator is the most common cylindrical projection

20 Conical

21 Conical Projections Best for continents in mid latitudes North America Europe Russia Not useful for a world map Unless several are put together

22 Planar or Polar (Azimuth)

23 Polar Projections Only one hemisphere Arctic Ocean in the northern hemisphere Antarctica in the southern hemisphere Not good for mid latitudes, low latitudes don t show at all

24 Compromise Projections Minimize distortion in one aspect AND Keep the most accuracy in other aspects Mollewide Robinson Goode s Homolosine (interrupted)

26 Robinson Mercator Distortion Compared Mollewide

27 Scale All maps have a scale Scale relates map size to actual earth size A scale of 1:10,000 means that one unit of measurement on the map will equal tenthousand of the same units on the surface of the earth

28 Legend The legend is the key to reading the map Defines the colors and symbols Map scale will be in the legend or at the bottom of the map Ratio 1:10,000 Fractional 1/10,000 Words One inch equals ten-thousand inches Graphic looks like a ruler

29 Large Scale vs. Small Scale A large scale map portrays a small part of earth s surface City Campus Classroom

30 Cholera Map of London

31 City Map of Denver

32 A small scale map portrays a large portion of earth s surface World map the smallest scale of all 1:13,000,000 is the scale of our wall map

33 Scale and Distortion The smaller the scale of the map, the larger the portion of earth s surface is being shown The larger the portion of earth s surface, the more curvature The more curvature, the more distortion will occur in transposing it to a flat map

34 Extremely small scale maps, like world maps, have the most distortion Large scale maps, like a map of the college campus, have little or no distortion

35 Types of Maps Maps are generally made for a specific purpose

36 Road Map Roads, towns, cities, and other data useful for transportation Most familiar type of map to the average person But there are many other types of maps!

37 Political Show man-made divisions, such as the borders of states or countries

39 Political vs. Physical

40 Physical Show physical characteristics, like mountains, lakes, and rivers Often show elevation by color coding

43 Topographic Shows landforms and elevations in detail Contour lines - lines that connect places with equal value, in this case feet above sea level

45 Thematic These maps each have a special theme Physical Climate Ocean Currents Biomes Cultural Population Ethnicity Income

47 Map of World Population

Earth Coordinates & Grid Coordinate Systems

Earth Coordinates & Grid Coordinate Systems How do we model the earth? Datums Datums mathematically describe the surface of the Earth. Accounts for mean sea level, topography, and gravity models. Projections