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

Maps Chapter 2

Overview The Grid System Map Projections Scale Types of Maps Remote Sensing Geographic Information Systems

The Grid System Poles Equator Latitude Longitude

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

Latitude (Continued) Prime Meridian Other meridians Passes through the Royal Observatory at Greenwich, England Selected at an International Conference in 1884 Other meridians True N-S lines connecting the poles Farthest apart at equator

Longitude Angular distance east or west of the Prime Meridian International Date Line generally follows the 180th meridian Distance between lines decreases towards the poles Time depends on longitude Each time zone ≈ 15° of longitude

Other Grid Systems Universal Transverse Mercator Township & Range system Land Ordinance of 1785 First used in eastern Ohio 36 mi2 divided in 36 squares of 1 mi2 (640 acres) Divided into quarter sections of 160 acres See Figure 2.4

Map Projections Transforming a globe surface to a flat surface always results in distortion Properties of Map Projections Area Shape Distance Direction

Area Equal-area or equivalent projections represent areas in correct proportion to the earth’s area But, the shape of the area is distorted to achieve this See Figure 2.5

Shape 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 Distance relationships are almost always distorted on a map 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 See Figure 2.9 A map cannot be both equidistant and equal-area

Direction Directions between all points cannot be shown without distortion Azimuthal projections enable a map user to measure the distance from a single point to any other point Azimuthal projections may also be equivalent, conformal, or equidistant

Types of Projections “Developable Surfaces” Globe properties 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

Cylindrical Projections Mercator Projection A lot of distortion towards the poles Shapes are fairly accurate, but areas are widely distorted Rhumb lines

Conic Projections The cone is closest in form to ½ of a globe Conic projections are widely used to depict hemispheres or smaller parts of the earth See Figure 2.8a

Planar Projections Plane tangent to the surface Planar projections are equidistant from the tangent point Commonly used for polar areas Gnomonic projections show all great circles as straight lines See Figure 2.10

Other Projections Goode’s Homolosine Robinson Ovals, hearts, trapezoids, stars, etc.

Scale Ratio between the measurement of something on a map and the corresponding measurement on the earth Represented in three ways Verbally Graphically Representative fraction (RF) 1:25,000 or 1/25,000

Scale (continued) Large-scale maps show a small area Very detailed Small-scale maps show large areas Very generalized

Types of Maps Topographic Surface areas in relatively high detail Physical & human features USGS quadrangles NRCAN in Canada Contour lines & intervals Shaded relief

Types of Maps (continued) Thematic Maps Point symbols Dot density Proportional circles Area symbols Usually different colors or patterns Choropleth maps Line symbols Non quantitative, such as roads Quantitative, such as isolines Flow-line maps

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

Satellite Imagery Landsat SPOT First launched 1972 Multispectral scanners (MSS) Thematic mapper (TM) SPOT

Geographic Information Systems (GIS) Five major components Data input Data management Data manipulation Analysis functions Data output