Chapter 2– Representations of Earth

cartography

the science of mapmaking

reference map

a map that shows a wide variety of general information, useful as a reference for looking up locations, place names, and other geographic characteristics of an area

thematic maps

a map designed to present information or data about a specific theme, as in a population distribution map, a map of climate or vegetation

think geographically

giving some thought to recognizing geographic patterns, understanding why they exist, and considering their significance

oblate spheroid

Earth’s shape– a slightly flattened sphere

great circle

circle in any direction formed by dividing Earth into two equal hemispheres; the plane of a great circle passes through the center of the globe. A route following a great circle that passes through two places marks shortest distance between those locations.

hemispheres

half of a sphere

navigation

the science of location and finding one’s way, position, or direction

coordinate system

a precise system of grid lines used to describe locations

equator

great circle of Earth midway between the poles; the zero degree parallel of latitude that divides Earth into the Northern and Southern Hemispheres

latitude

angular distance (distance measured in degrees) north or south of the equator

sextant

navigation instrument used to determine latitude by star and sun positions

prime meridian

half of a great circle that connects the North and South Poles and marks zero degrees longitude

longitude

angular distance east of west of the prime meridian

decimal degrees

angular degrees with fractions expressed as tenths, hundreths, etc.

the geographic grid

lines of latitude and longitude form the geographic grid

parallels

circle on the globe connecting all points of equal latitude

meridians

a line of longitude that forms half of a great circle on the globe and connects all points of equal longitude; all meridians connect the North and South poles

Solar noon

the time of day when the sun angle is at a maximum above the horizon

principal meridians

one of many lines running N–S (meridians of longitude) designated by the U.S. Public Land Survey System for locating plots of land north or south of these meridians

base lines

east-west lines of division in the U.S. Public Lands Survey System

Global Positioning System (GPS)

United States system that uses satellite data to locate positions and travel routes anywhere on Earth

map projection

any presentation of the spherical Earth on a flat surface

planar projection

map projection in which grid lines are transferred onto a plane or flat surface; planar maps are most often used to show the polar regions, with the pole centrally located on the circular map, displaying one hemisphere

conic projection

map projection achieved by transferring a spherical area onto a cone

Mercator projection

preserves compass direction but greatly enlarges areas near the poles

conformal maps

a map using a projection that maintains the true shape of small areas on Earth’s surface

equal-area maps

a map created with a projection that preserves correct proportional sizes for any given areas of Earth’s surface

legend

key to symbols used on a map

map scale

ratio between a distance as measured on Earth and the same distance as measured on a map, globe, or other representation of Earth

graphic scale

a ruler-like device placed on maps for making direct measurements in ground distances

magnetic declination

horizontal angle between geographic north and magnetic north

bearing

an angular direction of a line, point, or route measured from north or from a current location to a desired location

discrete data

numerical or locational representations of phenomena that are present only at certain locations—such as earthquake epicenters, sinkholes, and tornado paths

continuous data

numerical representations of phenomena that are present everywhere–such as air pressure, temperature, and elevation

isolines

a line on a map that represents equal values of some numerical measurement such as lines of equal temperature or elevation contours

topographic contours

line on a map connecting points that are the same elevation above mean sea level

contour interval

vertical distance represented by two adjacent contour lines on a topographic map

profile

a graph of changes in height over a linear distance, such as a topographic profile

gradient

a term for slope often used to describe the upstream/downstream angle of a streambed

remote sensing

collection of information about the environment from a distance, usually from aircraft or spacecraft—for example, photography, radar, and infrared

spatial resolution

size of an area on Earth that is represented by a single pixel

passive systems

remote sensing systems that record the natural reflections or emissions of energy from a surface

active systems

remote sensing systems that emit their own energy source and record reflected returns from surface features

sonar

a system that uses sound waves for location and mapping underwater

radar

radio detection and ranging

weather radar

radar that is used to track thunderstorms, tornadoes, and hurricanes

lidar

an abbreviation for “light detection and ranging,” a system that uses lasers to scan and image landscapes– a remote sensing system

draping

overlaying a digital image over a digital elevation model of a landscape

equal-area projection

preserves relative area but distorts shape

conformal projection

preserves local shape and angles but distorts area

compromise projection

balances multiple kinds of distortion

gnomonic projection

shows great-circle routes as straight lines

rhumb line

crosses meridians at a constant angle; easier to follow but usually longer

multispectral imagery

uses a few broad wavelength bands

hyperspectral imagery

uses many narrow wavelength bands