Ch.2 Portraying Earth

A globe is a true representation of earth

Maps

-flat representations of earth

-portray distance, direction, size, and shape two dimensionally

thematic maps-

Essentials for a Map:

-title, date, legend, scale

-direction shown by grid or compass arrow pointing north

-location, data source, projection type

Conveying Information on Maps:

Isoline-any line that joins data points of equal value of something

Characteristics of Isoline

-always closed lines

-cannot cross each other

Interval-

-change gradient shown by spacing of lines

Important types of Isolines

elevation contour lines-connect points of equal elevation on topographic maps

isotherms-connects points of equal temperature

isobars-connects points of equal atmospheric pressure

isohyet-connect points of equal of quantitues of percipitation

isogonic lines-conects points of equal magnetic declination

Map Distortions

-no map can be perfectly accurate, all have distortions

-size of the area being shown and the scale of the map

Map Scale

Map Scale is the relationship between the distance measured on the map and actual distance on Earth surface

-scale is used to measure distance, determine size area, and compare sizes

-distortions mean scale can never be exactly correct over full map

-larger areas have greater distortions

Scale Types:

Graphic

-line marked off in distances represents actual surface distance

Fractional

-conveyed with a fraction or ratio

Representative Fraction-

Verbal

word scale-the distance relationship in words

Large Scale and Small Scale

Large Scale-a relatively large fraction used to show a small portion of earth’s surface in great detail

Small Scale-a small representative fraction used to show relatively large areas but limited detail

The greater the detail the greater the scale

Map Projections and Properties

Cartographer-

Map Projector-a system by which earth curved surface is transformed for display on a flat surface

all projections have distortions

-carographers control or reduce one or more

Equivalence-a correct size ration of corrresponding areas maintained over entire map

-distorts shapes, notably on small-scale maps

Conformality-maintains proper angular relationships acroos entire map

-distorts size to depict proper shape

-impossible to depict true shapes for large areas

-conformal map of the world would enlarge hgh latitude landmasses

Compromise Projections

-equivalence and conformality cannot be maintaned on same projection

compromise map projection-neither equvialnce nor conformal

-balance reasonable accurate shapes with reasonable accurate areas

Families of Map Projections

Cylindrical Projections

“wrap“ globe in a cylinder tangent to the equator

-size distortion is the greatest away from circle of tangency or standard parallel

Circle of Tangency-

Standard Parallel-

Mercator

The Most Famous Projection

Mercator Projection-conformal cylindrical projection was designed for oceanic navigation

Loxodrome-a line on a sphere crossing all meridians at the same angle, represents a line of constant compass direction

Gnomic Projections-

Planar Projector

-obtained by projecting a globe onto flat surface at single point of tangency

-equivalent projection

-distortion increases outward

-typicallly show only one hemisphere or specific regions

Orthographic-view of the earth from space

Plane-

Azimuthal-

Zenithal -

Conic Projections

Projecting the globe onto a cone wrapped around a portion of the surface

-apex of cone is positioned above the circle of tangency where distortion is smallest

-best suited to midlatitude regions of east-west orientation

-particulary well adpated for mapping relatively small area

Pseudocylindrical Projections

A mix of conformal and equivalent in near football-shaped map

-Also called an elliptical or oval projection

-centeral parallel and central meridian cross at right angles

-centeral intersection, a point of no distortion

-minimize distortion of continets by intterupting oceanic regions

Goode’s interrupted homolosine equal-area projection is equivalent though not conformal and maintains shapes of continental coastlines even at high latitudes

Conveying Information on Maps

Elevation Contours-

-topographic maps have transitioned from paper to electronic

Digital Elevation Model

Digital elevation models are shaded relief, computer generated images derived from percise elevtaions complied in detailed databases

Global Navigation Satellite System

-is a system of satellite technologies that provide precise location data for points on earth surface

GPS-global position system in the US

GLONASS-russia’s global navigation satellite system

Galileo-Europe

Beidou-China

-each staellite continuously transmits positioning data

-receivers on the ground connect with at best four satellites

Trialateration-three dimensional coordinates calculated

Wide Area Augemntation System(WASS)-developed by US FAA for aviation

-network of grounf based reference stations monitor and correct GPS signals

Continously Operating GPS Refrence Station(CORS)

-NOAA manages a system of permanent and highly accurate GPS receiving stations

-constantly monitor change in ground surface by slight differences in latitude, longitude, and elevation

GPS Modernization Program

-newer satellites with greater accuracy

-civilian broadcast signal

GPS Applications

-since the 1980s, scientfic and commerical applications for outnumber of military uses

-gpps display of latitude and longitude with greater accuracy, cordinates frequently reported in more detail

Remote Sensing

Remote sensing-any measurement by a device not in contact with earth’s surface

-revolutionzied by satellites

Geosychronous Orbit-low orbit

Aerial Photographs-

Photogrammerty-

Orthophoto Maps

-multi-colored, distortion free photographic maps

-prepared from areial photographs

-show landscapes in greater detail while retaining common scale to measure distance

Visible Light and Infrared Snesing

-utlizing wavelengths of relctromagnetic radiation emitted by the sun and other obejcts

-visible light, xrays, ultraviolet, infrared and radio waves

Color Infrared-uses electronic sensors or photographic film to detect near infrared wavelengths

-false color of living vegetation as red

Thermal Infrared-wavelengths cannot be sensed with conventional cameras or photographic film

-thermal scanning measures radiant temperature and yield photographic like images

-useful for showing temperature differences in rock, water, and surface air

Multispectral Remote Sensing

-most satellites

-detects and record many bands of the elctrommagentic spectrum

-conveyed as a matrix of numbers each representing a value per pixel and band

Landsat

-originated at NASA

-curerntly there are seven orbiting satellites

Earth Observing System

-Terra and Aqua circle the earth

-collect range of data values and prduce numerous images

Commercial High Resolution Satellites-very high resolution imagery using small lower cost satellites

Radar, Sonar, and Lidar

Passive Systems-

Active Systems-

Radar-

Radio Detection-

Ranging-

Sonar-sound navigation

Lidar-reflected laser light to measure distance

Geographic Information System(GIS)-computer systems designed to analyze spatial data

-maps as searchable, visual libraries of spatial data

-location coordinates link a variety of data sources

-data layers can be crossed refrenced