Introduction to Geography Arthur Getis Judith Getis Jerome

Introduction to Geography Arthur Getis, Judith Getis, & Jerome D. Fellmann

Maps Chapter 2

Overview l l l l Maps as the Tools of Geography Locating Points on a Sphere Map Projections Scale Types of Maps Remote Sensing Geographic Information Systems

Maps as the Tools of Geography l l Primary tools of spatial analysis Cartography: the art, science and technology of making maps

The Grid System l l Poles Equator Latitude Longitude

Latitude l l Angular distance north or south of the equator Measured in degrees l l l 0°-90° North or South Each degree of latitude = 111 kilometers (69 miles) Minutes (’) and seconds (”)

Longitude l Angular distance east or west of the Prime Meridian l l l 0°-180° East or West Distance between lines decreases toward the poles Time depends on longitude l l Each time zone ≈ 15° of longitude International Date Line

Other Grid Systems l Township and Range system l Survey lines oriented in the cardinal directions l l l Base lines run east-west Meridians run north-south 36 mi 2 divided in 36 squares of 1 mi 2 (640 acres) l Divided into quarter sections of 160 acres

Global Positioning System (GPS) l Data provided by orbiting satellites l l l Maintained by the US Department of Defense Continuous transmission of position and time signals GPS receivers use satellite data to determine precise measurements of a specific location Military Use Civilian Use

Map Projections l l Earth can be represented with reasonable accuracy only on a globe Globe properties l l l All meridians are equal in length All meridians converge at the poles Lines of latitude are parallel to the equator and to each other Parallels decrease in length as one nears the poles Meridians and parallels intersect at right angles The scale on the surface of the globe is the same everywhere in all directions

Map Projections l Transforming a globe surface to a flat surface always results in distortion of some or all of the four main properties of actual earth surface relationships: l l Area Shape Distance Direction

Area l l Equal-area or equivalent projections represent areas in correct proportion to the earth’s area Shape of the area is distorted to achieve this l See Figure 2. 6

Shape l l l No map can provide correct shape for large areas, but some can accurately portray shapes for small areas Maps that have true shapes are known as conformal A map cannot be both conformal and equivalent (equal-area)

Distance l Distance relationships are almost always distorted on a map l Some maintain true distances along one direction or along certain lines Equidistant projections show true distances in all directions, but only from one or two central points l A map cannot be both equidistant and equal-area l

Direction l l l Directions between all points cannot be shown without distortion Azimuthal projections show true directions from one central point to all other points Azimuthal projections may also be equivalent, conformal, or equidistant

Scale l l Ratio between the measurement of something on a map and the corresponding measurement on the earth Represented in three ways l l Large-scale maps show a small area l l Verbal Graphic Representative fraction Very detailed Small-scale maps show large areas l Very generalized

Types of Maps l General Purpose or Reference l Topographic l l l Surface areas in relatively high detail Physical and human features Relief (elevation) is shown using § § l Contour lines and intervals Spot heights Bench marks Shaded relief Thematic or Special Purpose

Map Symbols l Various symbols represent qualitative or quantitative data l Point symbols l l l Area symbols l l Location of features, such as airport, city Quantitative, such as number of farms, size of city Usually different colors or patterns Choropleth maps Cartogram maps Line symbols l l l Qualitative, such as roads Quantitative, such as isolines Linear movement, such as flow-lines

Remote Sensing l l Detecting the nature of an object from a distance Aerial photography l l l Orthophotomaps False-color images Nonphotographic imagery l l l Thermal scanners Radar Satellites

Geographic Information Systems (GIS) l Assemble, store, manipulate, analyze and display geographically referenced information l l l Database of digitally recorded geographic information from variety of sources Computer displays any combination of data showing relationships among variables Used in all professions